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# MA008 Lesson 2 Expressions

Contents

## Excitement About Wipers & Nozzles

People were so excited about Grant's new product that he started getting requests left and right for his glasses wipers and spray nozzles. So, he started to keep a list of everyone who would want a pair very soon. By the end of 1 day, 36 of his friends had begged him for glasses wipers and 11 of those people each said that they would also like a pair of nozzles to go with their glasses wipers.

## Total Earned

Once he realized how many people were excited about his new business, Grant started to wonder how much money he could bring in. So assuming that Grant only sells glasses, wipers, and nozzles, which of these 4 expressions do you think should replace the question mark to make an equation for the total amount of money that he'll earn.

## Total Earned

Well, unless Grant plans on paying other people to buy his products, he'll presumably bring in some money each time he sells a nozzle, and each time he sells a set of wipers. This means that the money he earns is going to be equal to the money he makes from his wiper sales plus the money he makes from the nozzle sales, which is just this first choice up here. For example, let's say, just picking numbers out of the air, that Grant decides to sell a wiper set for \$5 and one nozzle for \$3. Well, then we know that money earned at that point would be equal to \$5 plus \$3 or let's see, if I was going to pay for these, it would be 5, 6, 7, \$8 total. So all we would do to find the total money earned would be to add the cost of each of the products together.

## Incorporating Price

So, we decided to call the price per wiper set w. That means that if Grant sells one set of wipers, he'll earn w dollars. If he sells two sets, he'll earn w+w dollars, which is 2w dollars. If he sells three sets, he'll earn w+w+w, or 3w, and so on and so forth. Since you know that he is going to sell 36 wiper sets, that means he's going to make 36w dollars off of the wipers along. So, 36w is the correct answer.

## Nozzles

Now that we've dealt with our money from wipers, let's move on to figure out how much money Grant's going to make, from selling this first batch of nozzles. Remember that, 11 people, each asked him for two nozzles. Also, we decided that n is equal to the price per nozzle. This is for one nozzle, not for two nozzles. So, which of these choices do you think is equal to the money he is going to earn from these nozzle sale so far?

## Nozzles

So part of figuring out how to solve word problems well is figuring out what information isn't important for the question that we're trying to answer. We want to know how much money Grant's going to make from selling nozzles. All that this is going to depend on is the price per nozzle and how many people want to buy nozzles. That means that these answers with 36, which has to do with the people who want to buy wipers are irrelevant for this question. Also w is the price per wiper set not per nozzle, so this answer which depends on w can't be correct. And this one even though it also involves an n, involves a w so, it can't be right either. We're only focusing on nozzle sales here. So what are we left with 11, pretty good nothing having to do explicitly with wiper sales. However, these 2 answers 11 and 22 don't involve an n. That will mean that no amount or how many nozles Grant sells, he's going to make either just \$11 or \$22. I would hope that, for his sake, the more nozzles he sells, the more money he makes so we want to say that those answers aren't correct. So now we have 112n and 11n. The key here is remembering that each of these eleven people want two nozzles. Not just one nozzle. So each person who buys two nozzles is going to pay him not n dollars but 2n dollars. If 11 people paying 2n dollars so that means we need 112n which is this answer right here.

## Writing Concisely

So from our last two quizzes, we now have developed a new expression for total money earned by Grant. Instead of money from wipers, we have 36w, where w is the amount that each set of wipers cost. And instead of money earned from nozzles, we have 11 person pays for one nozzle. Now when I look at this term 11 2n, it looks a little bit complicated to me, definitely more complicated than 36w does. Can you think of a simpler way to write 11 2n? Now, there are a ton of different ways that we can write 11 2n and come up with a mathematically equivalent expression, but I would prefer that we try to come up with a simpler way to write this. So, if you have an idea of how to do that, please type it into this box right here.

## Writing Concisely

So one way to look at the term 112n is to think that we're adding 2n to itself 11 times. Okay great, we have 112ns added together. However we know that 2n is just equal to n+n. So we can write this yet another way. For each 2n we can instead write n+n, so we end up with n+n plus. So, for every 2n that we had in this equation, I wrote n+n instead. Now I actually already counted all these n's up and it turns out that there are 22 of them. So we know that So apparently 112n is equal to 22n. That means that we can come up to our equation for the amount of money that Grant is going to earn and replace 112n right here with 22n.

## Factors

Writing up and counting out those 22 n in the last quiz took me a really long time, though I can only imagine how torturous it would have been if I had, had to multiply there is a much easier way to simplify terms than adding them together like we did then. To talk about how this works, let's start by considering a term. Lets say, 5x 7y 2z. Now remember, a term is a bunch of variables or numbers, or both, that are multiplied together. And before we start playing around with this term, I'd like to add one more word to our vocabulary, factor. Now, factors are things that we multiply together. Just like terms are things that we add together. Together. So this term, 5x 7y that are all multiplied together. Another way to think of a factor, is that it's something that a term is divisible by. Now, we can't forget that in this term there are invisible multiplication signs between the five and the x, the seven and the y, and the two and the z. So another way to think about this term is that it's

## Identifying Factors

So real quick, let's just have a quiz. Which of these choices down here is a factor of this term, 5x 7y 2z? Remember, you can think of a factor as something that this term is divisible by, or as something that you can multiply by some other set of factors to equal this term. Please check as many answers as you think

## Identifying Factors

So, let's just go through these entries one by one you to figure out which ones are correct. Starting of 2z, we see that this is something that is multiplied by 5x and by 7y in order to equal this term. So, this is definitely a right answer. Now, when look at five, we need to remember that invisible multiplication sign between the five and the x. If we multiply five by x and 7y in 2z, then we get this whole term, so five is also a factor. Now, one is where things get a little bit tricky, and if you miss this one, not a big deal. This actually is a factor of this term and actually of any term. The reason that one is a factor for any term we might have, whether it's a number or a variable, is because, if you multiply one by that term itself, you will end up with the term that you're looking for. So in our case, the thing that we need to multiply one by in order to get 5x7y2z is just this term itself. I know that might seem a little bit complicated right now, but you'll have plenty of practice in the upcoming quizzes to sort this all out. Bottom line, one is always a factor. Now, first, you might think that zero is similar to one in this way, but zero is actually not a factor here. We can't divide this expression by zero, that would actually give us a solution that we don't know how to interpret right now. And there's nothing that we can multiply by zero in order to get this expression, since zero times anything is just equal to zero, so zero should not be checked off. We know that y is multiplied by seven and also by 5x and check that one off as well and x works in the same way. So, we've checked everything off except for the zero. That was great. I know that factors are a little bit trickier than terms, so I hope that this vocabulary word is starting to make a little bit of sense. We'll keep using it really frequently.

## Commutative Property

So now that we understand what factors were multiplied together to create this term, is there a more simplified way for us to write this? Thankfully the answer is yes. However before we can start to play around with this term, we need to learn about something called the commutative property. Specifically the commutative property of multiplication, since all of our factors are multiplied together here. The commutative property of multiplication basically tells us that it doesn't matter what order you multiply things together in. So, for example we know that 2 3 = That means we know that 2 3 is just = 3 variables instead of with numbers we could talk about, let's say, x z y. Here we have three different variables multiplied together and we can rearrange these factors in any order we want and still get a mathematically equivalant expression. So we could have, a ton of different things maybe z x y. That's also = y x z or z y x., and so on and so forth. All these expressions and all the other ones that we could get, by rearranging these in other ways are equal to one another. So remember for multiplication, it doesn't matter what order you multiply things together in. This holds no matter how many things you want to multiply together, and it holds whether the factors are variables or numbers.

## Commuting

Okay, time for a quiz. Now that we've talked about the commutative property of multiplication. Let's see if you can apply it when we're dealing with this term right here. 10m237. I would like you to check off all of the expressions down here that are equal to this term. Just a hint, there are probably going to be several that are right answers.

## Variables on the Right

So going back to this term that we're looking at earlier 5x7y2z, we can start to use what we just learned about commutativity to rearrange all the factors that are multiplied together here, in whatever way we want to. Now, what I really want in this case is for all the variables to be on the back end of the term and all of the numbers. Are the constant factors to be at the front of the term. So please write in these slots an equivalent version of this term by filling in each slot with either a constant or a variable. So, we're just going to rearrange these terms in an order like this. Think about what answers are allowed because of the commutative property.

## Variables on the Right

Looking at this term, the constant factors are five, seven, and two. So, we can write those in the first three slots right here. Because of the commutativity of multiplication it doesn't matter what order we write the five, seven, and two in. Instead, I could have writen two, seven, five or two, five, seven or seven five two or any order of these three numbers in these first three slots. For simplicity sake, I'm just going to leave mine written this way, but you're answer is right as long as these three constant factors are in these first three slots. Now, what's left over to deal with are the variable factors. So for those, we have x, y and z. Here, it's important to remember, the invisible multiplication signs between these constant factors in the adjacent variables. Remembering that those are there is what's going to allow us to pull out the variables and move them around. So, I'm just going to keep x, y, and z in the order they're written in and fill them into the slots right here. Now, just like with the constant factors, we could write these variables in any order that we want to. We could write z,y,x, z,x,y, x,y,z, actually, that's what we have, [LAUGH] y,x,z, . Any order these three variables go in is correct as long as they are in these last three slots.

## Make it Pretty

So now this is what our term looks like. 5 7 2 x y z. Now this definitely looks different from how our term originally did, but I wouldn't say that it looks less complicated. So our goal for this quiz is to make this look much more simple. So think back to when we were talking about Grant's gleaming glasses last time. We simplify this term 11 2n to equal 22n. We are using the same idea that we used to come up with that answer. Can you think of a way to simplify this term up here. Try this question down as much as you can and remember to get rid of any multiplication signs that you don't think need to be expressive.

## Make it Pretty

The first thing that I notice when I look at this version of our term is that we actually don't need these dots between the variables. And actually, we don't need a multiplication sign between 2 and x either. Inside a term, the only place we really need to explicitly indicate multiplication with the multiplication sign is between the constant factors. The reason that we had to really write them in between the 5, the 7 and the 2 before, was so this didn't look like we were writing get rid of those three unnecessary multiplication signs. Remember, if you kept them in, your term is still mathematically correct, it just contains a couple of extra symbols that don't necessarily need to be there. So now we have this 5 7 2 to deal with. Those are just numbers, and we know how to multiply numbers together. 5 7 = 35. And with 70, and write the remaining factors afterward, xyz.

## Simplifying

So now that we've worked step by through how to simplify terms, I want to you to try simplifying this term on your own. So in this box to the right, please write the most simplified version you can find of (-5s)(2r)(3t). Remember that theses parentheses just indicate multiplication. It's not that means that negative 2r is being multiplied by -5s and by 3t, not subracted from them. Good luck.

## Simplifying

Like we did before, we're going to start off by identifying the constant factors in this term, and then moving them to the front of the term. So our constant factors here are negative five, negative two, and three. So you can write -5-23 as the first three factors of our rewritten version of this term, then after that come the variables s, r, and t, so we multiply the constant factors by the variable factors. Remember that these multiplication signs between the variables actually aren't necessary, so I'm just going to get rid of those right away. Now negative five times negative two is just positive ten. Remember, a negative times a negative equals a positive. So then we have, 103 and 103 is just equal to 30. So we can replace, -5-23 with 30, and then multiply that by the rest of the factors that are left over s r t. So our final simplified version of this term is easier to deal with than this initial version of the term did. So I think we're making really good progress toward simplifying different expressions.

## Alternative Forms

So, I've already showed you one convention that we use when we simplify terms. We put the constant factors at the beginning of the term. When we do that, it makes it easy once we simplify because we end up with one coefficient and then all of the variable factors after it. People also tend to put the variable factors in alphabetical order. So, if you wanted to do that, we could say that this also equals 30rst. In order to make the change from 30srt to 30rst, we had to remember the commutative property of multiplication. Since we were allowed to switch the order of r and s without changing the value of this term. So, the order that variable factors are written in is just another convention in algebra. It's just something that's useful for us to use, but it doesn't change the fact that this version of the term that we had initially is mathematically equivalent to either of these other two simplified versions.

## More Simplification

Let's do one more quiz to practice simplifying terms. This time please simplify 4x y-3x. Remember that this negative sign right here, in front of the 3, is part of the factor -3. We're not subtracting 3x from y, we're multiplying 4xy by -3x. So keeping that in mind, please write the most simplified version of this term that you can over here.

## More Simplification

So as always, we're going to start to simplify this term by identifying the constant factors in it. So for those, we have 4 and -3. And remember, we want to move those to the front of the term, so that they are the first two factors that we have written. So this term is equal to have left over, x, y and x. So right off the bat we know how to deal with 2 of the factors here. We know that 4 -3 is just equal to -12. So we can replace 4 -3 with -12 and then write the 3 remaining factors. There's something interesting here though. We have 2 variables that are the same. We have x and x. I'm going to rewrite this one more time with the order of the variables switched so that the x's are next to each other. That's just generally a good rule of thumb in algebra is to write things that you think are related to one another next to each other. This x x is interesting. This is the first chance that we're going to get to use exponents. You've seen them already a few times in this course, but we haven't gotten to write our own factors with exponents in them. So, this may seem like new material or it may be review for you, but xx can also be written with an exponent as x^2. In the same way, x x x = x^3, and so on, and so forth. Remember that in all of these equations right here, I didn't need to write any of these multiplication signs. If we had just written the x's directly next to one another, without any symbol in between, multiplication would still have been implied. So instead we could just have xx equals x^2. I just wrote this out to be abundantly clear. The exponents show how many of the same factor are multiplied together. Incidentally if 2 x's mulitiplied together is equal to X^2 then when we have just 1x is equal to x^1. This seems a little bit silly to write though, writing X to the 1 is more complicated than writing just x so. We usually don't move from having x to writing x to the first instead. So using this information about exponents, we can replace this x x with an x^2. And with thta information we can rewrite this term as -12x^2y. We're obeying all the conventions we know about how to write terms because we have the constant factor at the front, and then we have our variables in ascending alphabetical order. We have the x^2 before the y. That was awesome, I know that this was a pretty complicated thing that involved a ton of different concepts, some of which we haven't focused on a lot yet. But don't worry if exponents still don't feel totally comfortable, we're going to keep working with them a ton more.

## What is a

So now that we know how to simplify terms, we can get back to Grant and his gleaming glasses. Earlier, we came up with expressions for the amount of money that Grant's going to make from his friends buying his wipers, and also from them buying his nozzles, and we had an equation for the total amount of money earned. Saying that the total amount of money that he's going to earn from his friends is equal to the amount that they spent on his wipers plus the amount that they spent on his nozzles. Now I'm going to add one more equation into the mix for you or rather create one more variable. Total money earned right here takes a long time to write, so instead I'm going to call this a different variable. Let's say a. So, with my other equations up here, I can also write total money earned euals a. So, let's combine all this information that we came up with in our earlier quizzes and the new information that I just gave you that a stands for the total amount of money earned. Which of these expressions down here, do you think should replace this question mark, in this equation for a? You can check as many answers as you think are right. I know this is a lot to look at on the screen at one time, but once we come up with this final equation, we'll only have single letters and numbers, and no more words, in our equation, and that will make things much easier for the future.

## More Orders For Grant!

So now we have this wonderful straight forward equation for the amount of money that Grant's friends are going to pay him once they buy their glasses, wiper, and their spray nozzles. However just when we think we're starting to figure things out for him situation gets a little bit more complicated. Even though this means more work for us, this is great for Grant, because more of his friends have asked if they can buy his products. The day after his first round of requests came in, even more of his friends and his friend's friends heard about his new incredible inventions, and asked him to add to them, to the list of people to buy his products. and 25 more people wanted to buy 2 spray nozzles each. This equation no longer tells us the total amount of money that Grant's going to earn from his friends, and his friend's friends buying his wipers and nozzles. So, what we need to do is create a new equation. We need to come up with a different way to express a that takes into account this new information that we have, but also doesn't forget what we had before.

## More Customers

We heard a lot of information in the last video, so here is just a summary of all of that on one screen. We can think about Grant's sales story so far as having 2 situations. The situation after the first day, which I'm going to call the before picture and the situation after the second day of selling, which is the present situation we're concerned with. The last equation that we came up with, a = 36w + first day. So, I changed the name of the total money earned to a old to show that this is the money earned after the first day of selling. This equation still works if we're only interested in calculating the money that Grant earned from his friends after just that one day, but now, we want to find, is what I'm going to call a new. The money he's going to get from those people and from these new people who also want to buy. What we're going to do in this quiz is come up with an equation for anew, which should combine the information from aold with this new data about people who are also going to buy the wipers and nozzles. So, which of these equations down at the bottom is the correct equation for anew? The total amount of money that Grent will have after these people on the first day buy his wipers and nozzles, and these people from the second day buy his wipers and nozzles. This is alot of information to take in, so I'm going to lable this quiz a challenge quiz. Actually many of the quizzes that you've had have been challenging, but I think that this one is especially difficult. Think really carefully about how many terms you think this new equation should have. Should it have 2 terms or should it have 4 terms? Also, there may be more than 1 correct answer. Even if you don't get it right the first time, just give it another shot.

## Gathering Terms

As I said in the past several videos and quizzes, there are a ton of mathematically equivalent ways of writing any expression we might have. For example, if I rearrange the factors within any of the terms here, or rearrange the order of the terms themselves, or let's say, tack on a 0 at the end. The value of the expression on the right side of the equation doesn't change. However, there are certain convienient ways of writing expressions. Ways that actually make them simplier to deal with that we're going to want to use. We call this process of rewriting expressions; simplifing expressions. One really useful tool that can help us start to simplify and expression, or see if we can simplify it any further, is to change the order of the terms. We know that we're allowed to do this because of the communitive property of addition. So, how could we do that here? Let's just rearrange the terms on the right side of this equation so that both terms containing w are in the first two slots and the two terms containing n are in the last two slots. So please just type the proper terms into the proper slots. These smaller spaces are for plus or minus signs but you can also type in as you see fit.

## Gathering Terms

So hopefully, this quiz is a little bit easier than the last one we did. What we're trying to do first is just identify the terms that have w in them. So, going through our equation up here, we see 36w and 51w, and we can just fill those in to these first two slots. Remember that it doesn't matter which order we write them in. It doesn't matter if we write 36w or property of addition. Next we need to identify the end terms, so those are the two that are left, 22n and 50n, and we just want to write those in these two slots. Again, order does not matter because we're just going to add everything together. I'm just going to put the 22n first since 22 happens to be my favorite number. The last step to make this a fully blown equation is to add in our plus or minus signs between the terms. Here in the top equation, every term is positive. You don't see any negative signs here. So that means that each of these signs is going to be a + sign. When we switch terms around, there's no change to the value of each term. Nothing's going to become negative that used to be positive. So the only thing that's different about this bottom equation from this top equation, is the order that we've written the terms in.

## Combining Like Terms

So now that we have this equation for the total amount of money that Grant's going to make from people who bought his products the first day and the second day, it would be great if we could simplify it further, however we don't know how to do that yet. So, before we dive into this particular example, let's look at a slightly less complicated but similar problem. Let's say we just have some expression. I picked 3x - 5y + 6x + 9y. Now how can we simplify this expression? Well, I think we need to remember what each of these terms really means. So 3x for example is actually equal to x + x + x and 6x is actually equal to 6 x's added together. Right now, writing this out might not seem particularly helpful. But I think the reason that I chose to write these terms this way will becomes clear if we just rearrange the order of the terms in this expression. So now we switch the order of the terms around so that terms with x are next to each other and the terms of y are next to each other. Now we can see that the first thing we want to do is add 3x and 6x together. With all of the x's written out, that doesn't seem that hard. I just need to figure out how many x's, total I have down here. And if I count them I have 1, 2, 3, 4, 5, 6, 7, 8, that, in order to get the sum of 3x and 6x here We don't actually have to count all the x's. All we really have to do is add the coefficients of the variables together, since 3 + 6 = 9. Once we have the coefficient, we just make sure that we multiply that by the variable that both of these terms have. We usually call this adding like terms, or combining like terms, as I've written at the top of the slide.

## Its Fine to Combine

Now that we've figured out how to combine figure out how to combine -5y and 9y? So just fill in the term that you think is necessary to make this equation true.

## Its Fine to Combine

Remember that in order to add 3x and 6x together, I simply added their coefficients, and then multiplied by the variable they both contain to get 9x. Since 3+6 is 9, and the variable in both terms is x. We can do the same thing to deal with the y terms over here. So, -5y+9y is going to be equal to whatever negative 5+9 is, times y. We know that -5+9=4, so our answer is 4y and we can fill it in the box. Over here in our original expression, we have four different terms. And over here, we only have two terms. This why we call this simplifying expressions. This expression is way more simple than the one over here is. Remember that I was allowed to put an equal sign here between these two expressions because they are exactly mathematically equivalent. In order to come up with the expression over here, I only played with the terms inside of this expression. I didn't bring anything in from the outside. The only way I modified it was by squishing together things that were already there.

## What to Combine

Since we've now had a little bit of practice with combining like terms, I want to make sure that it's abundantly clear which terms we're allowed to combine and which ones we're not. Terms that you're trying to add together can be combined if and only if two things are true. So first things first, the terms have to have exactly the same variable or variables. So examples of this will be terms like 3xy and 7xy or -4b and 15b. On top of this I have to add that each of these variables that correspond to another have to have the same powers or the same exponents. So, if we have the term 3x^2 and the term 6x, and we try to add those together, we cannot combine them. These are not like terms, even though they have x's in them, this is 3x^2 and this is just 6x to the first power. They don't have the same power, so we can't squish them down into 1 term. Another example of this would be something like 11ab^3 + 12a^2b3. Even if the b^3 factors have the same power, the a here only has a power of 1 and the a here has the power of 2. We cannot add these two things together because one of the variables involved does not have the same power in both terms. So, we cannot squish them down into one term.

## Practice

Now that we've talked explicitly about what it means to combine like terms, or combine terms that have the same variables with the same powers in the them, I'd like you to try an example of how to do this. Please simplify this expression, Start by figuring out which terms in this expression are like terms, and then figure out how to combine them. Good luck.

## Practice

Just like we did in the example, we're going to start by rearranging the order of the terms in this expression, so the terms with the same variable are next to one another. Great, now, we have 7x-10x+5y+3y. The next step is to add together the coefficients of the like terms. Great, so now we have -3x, since 7-10 is negative three and the variable there was x, plus make this a little bit prettier, since we have a negative sign at the front, we could because of the commutative property, rearrange the order of the terms one more time. So, I personally prefer to write it this way, 8y-3x. So this is our new version of the expression on the left. It's almost hard to tell from looking at these two expressions that they're actually equal to each other, but that just shows you how powerful combining like terms is. We end up with an expression that's much nicer to look at and much easier to use.

## More Practice

Now this time we have an expression thats a bit more complicated than the past few that weve seen. However, if we keep in mind our rules that we know for combining like terms, that we can only combine terms that have the same variables with the same powers, then this actually shouldnt be that much harder than the other ones that we've done. Just give it a try, write the simplest version of this expression that you can in this box over here.

## More Practice

The first thing we need to do in order to start simplifying this expression is to identify which terms are like terms. -5x^2 is the only term in this expression that has an x^2 in it so it is not like terms with anything else here. However, we have seem related to the x^2 term but remember, the power of the term matters. Both of these terms have x^1, remember, there are little invisible ones right when you just have a variable on its own. x is just equal to x^1. Anyway, these 2 terms are like terms, so I'm going to start to rewrite this expression with the like terms next to one another. Remember that the sign of the term, it belongs to the term itself, and moves along with it when we rearrange the order. Then, the 2 terms that we haven't written are 14 and -3. These are just numbers, so they're definitely like terms, and we'll keep them next to one another. Now, that we've identified which terms are like terms, it's time to combining those like terms. So, -5x^2 stays by itself, since we can't combine it with anything else. For the x^1 terms, we end up with a new coefficient of 6-1 or 5, so plus 5 times the variable, which is x. And then, all we have left to deal with are other numbers. 14-3 is 11 so we add 11 to the end. Once you've written down our final expression, we can check and make sure that none of the terms in it are like terms with one another. That is, we only have one term of each type in the final expression. This is an 2 term, this is an x^1 term, and this is a constant term. So, there's nothing more that we can combine. That means that we've reached the final stage of our simplification. Awesome.

## Simplifying Four Terms

By now you've had a lot of practice with simplifying expressions. So here's a sort of challenge problem for you. Please try to simplify x^2 + 3xy - 7yx - y^2. As always, type your answer into the box right here. Now this is definitely more difficult, or at least a little bit trickier than what I've asked you to do before, but just give it a try.

## Simplifying Four Terms

So, like we've done a couple of times before, let's start off by going through the terms one by one to see if any of them are like terms. x^2 right here is the only term with an x^2 in it, and -y2 right here is also the only term with a y^2 in it. However, we have these two middle terms that each have an x^1 and a y^1 in them. So, are they like terms? Well, according to our rules up here, they do have the same variables. And those two variables, x and y, have the same power. The x here is x^1, as is the x here. And the y here is y^1, as is the y here. So, presumably they are like terms. What we need to do is use the communicative property of multiplication that we talked about a long time ago to make these look the same. We know from the communicative property of multiplication that xy, or just xy, is equal to yx, or just yx. So, I'm going to rewrite this term right here, 7yx, as 7xy instead. It's amazing how switching around the orders of factors within terms can change the way an entire expression looks. Now, our job is pretty stand. The terms that we're not combining, I'm just going to write as they are, so x^2 is the same. And then, I'm going to combine these two terms in the middle. So remember, we add their coefficients. 3+-7 or 3-7 which is -4 times the variables x and y, -y^2, which doesn't change.

## Grants Equation

By this point, you've had a bunch of practice with combining like terms. So, let's go back to that last problem we were doing with Grant, and this is glasses, wipers, and nozzles. Here's the equation we had A, the total amount of money he's going to earn from his friends buying his products is equal to 36w+51w+22n+50n. Last time you saw this, we didn't know how to combine like terms, but now you do. So in this box I would like you to take the most simplified version of this entire equation that you can come up with. Remember, I am looking for the whole equation not just this expression. You need to include the a equals in the equation down here.

## Grants Equation

So, since we know we're trying to write an equation and not just an expression, I'm going to start off by writing a = in our box down here, since I know that the left side of the equation is not going to change at all. Then I can start to combine my like terms. Conveniently our terms with w are already written next to each other and are terms with n. It was so nice that we did that for ourselves earlier. This is pretty straightforward then. Since these are like terms, I can just add their coefficients. 36 + 51 = 87 and I multiply that by the variable w, 22 + 50 = 72 and that gets multiplied by the variable as well. Awesome, we're one step closer to helping Grant figure out how much money he's going to have after these first 2 batches of friends pay him.

## Put It Together

We've simplified terms by combining factors within them and we've combined like terms. So, let's try to do both of those things at the same time. Here, we have a very long expression, That took a really long time to write and a really long time to say, so it would be awesome if we could simplify this. That is what I would like you to try to do. Now if this looks daunting, no big deal. Just give it a try. You have absolutely nothing to lose. Writing your work on paper first will definitely help you. Also, remember to try to simplify within each term first, and then, once you've done that, to identify what the like terms are in this expression, then you can work on combining them together. Good luck.

## Put it Together

The first thing that I am going to do, in trying to simplify this expression, is to look at each of the terms and figure out if I can squish it down at all. So first we have 15x^2. There's nothing that I can do to make that more simple on its own, so I'm just going to rewrite it. Then, 3x^7, same thing, then I come to. -7x2x. Now there are definitely some factors here that I can, can combine. If I rearrange the order of these things I can put -7 and the end, -72 is -14. So I have a coefficient of -14. And then we have xx. We know that xx is just X^2. So I can write that as well. Moving on, we have -42x. We can, again,combine the two factors. So you have -8x, -54, 54 is 20, so we have -20+x3. We can just rearrange the order of those two, and then we have 3x, which is just terms, in and of itself, is as simplified as it can get. The next step is to figure out which terms are like terms. I'm also going to already start writing like terms next to each other in a modified version of the equation. We have 2x^2 terms, only just need to combine the terms that I know are like terms. Remember that we add the coefficients of like terms together, and then multiply by the variable. 15-14 is 1. So we have 1x^2, or just x^2, 3x^7 is on its own. It's not combined with anything else, -8+3 is -5, times the variable x, and then we have our constant term. So this right here is our final answer. Our long, not very pretty expression has been squished down to be something much more manageable.

## Polynomials

In the next few minutes, I'm going to throw a couple more vocabulary words into our mix. First, I want to talk about a special kind of expression, in fact, the kind that we've seen most up to this time. These are polynomials, a polynomial is an expression made up of constants, variables or both that are combined using division, subtraction, or multiplication. So this basically means that we have one 1 or more terms like we've talked about before added together. The variables and I suppose the constants as well in a polynomial, also have to have non-negative integer exponents. So as an example of a polynomial, we might have something like So some polynomials that we see will have more than one variable in them, like these two right here. But often times we'll also see polynomials that have just 1 variable involved, or maybe even none. So an example of that might be something like But again, any combination of constants and variables, using these operators, and only these kind of exponents makes a polynomial.

## Not Polynomials

So now that we've talked about what polynomials are, and seen a few examples of them, which of these expressions are not polynomials? Notice I want you to check the ones that are not polynomials, not the ones that are polynomials. Remember the three requirements that an expression must fit in order to count as a polynomial. I have listed them right here in case you need to check. And if you have trouble with this just go back and watch the last video to refresh yourself on what apolynomial is. Goodluck.

## Not Polynomials

Three of these are not polynomials, but the rest of them are. We learned that a polynomial is an expression that only uses addition, subtraction, and multiplication to combine constants variables. But this first trace right here has a big division sign in it, dividing one expression by another expression. Now if we had either the numerator or the denominator of this fraction on its own, then both of them would be polynomials. But because they're divided, this is not a polynomial, so we'll check that one off. We'll talk more about expressions that look like this later on the course. One of our other important rules is that a polynomial must have exponents in it that are only non negative integers. Right here we have x1/2 and 1/2 may be positive, but it's not an integer, so that means that this is not a polynomial. We can think about that rule again when we look at this answer choice right here, -6x^5+x^-3-11x+9. All of these terms in here are fine for being part of polynomials, except for this one x^-3, because -3 is a negative integer exponent, not a non-negative integer exponent. So that means this expression is not a polynomial. It may seem a little bit funny that 6 counts as a polynomial. We don't often talk about numbers or variables on their own as polynomials, but they technically do qualify since they do fit our definition. We said that polynomials could have just variables, just constants, or both. So 6 and all other constant terms are technically polynomials. We're going to talk about polynomials throughout the entire rest of the course, so it's great to get a handle on how to find them.

## Identifying Degree

We just said that the degree of return in a polynomial is the sum of all the exponents of all the variables in that term, so the degree is a number. Now knowing that, I would like you to write in each of these boxes, what the degree of the term next to them is. So just fill in the proper number in each of these blanks.

## Identifying Degree

Our first term right here only has one variable in it, x, and the power that x is taken to is four so that means the degree of this term is four. This is a fourth-degree term. Now this next one is a little bit tricky. 100 is just a constant term. It doesn't have any variable factors in it, or in other words, it has 0 variable factors. So, this means that its degree is 0. This is true of any constant term. If we had the number, say, 78 here instead or -432 or 19.3, any constant term no matter what it's value is has degree 0. So, that means that 1/2 over here, which is also a constant term, has a degree of that if we desperately wanted to have a variable in a constant term, but we didn't want to change the value of the term, what power would that variable need to be taken to? So, let's say, we have 1/2 here and we want an x in that term. In order to keep this term equal to 1/2, we need to have x be to the 0 power since anything, any variable, or any constant, to the 0 power equals 1. That means that we would actually have, 1/2 times 1, which is just equal to 1/2. But even if we choose to write the term in this way with the variable involved, the power of that variable is 0. This is still a zero-degree term. For this next term, y, we need to remember that any variable that doesn't have an exponent written explicitly, actually has an invisible one as its power. So, this term has a degree of 1. It's a first-degree term. And lastly, we have x^2, y^2, z^3. So, the degree of this term is just going to be 2+2+3, which is equal to 7.

## Degree

Now that you know what a polynomial is, we're going to talk briefly about a word that we can use to characterize a give term in a polynomial. The degree of a term. Now the degree of a term is equal to the sum of all the exponents of all the variables that are in that term. So if we have a term like -4x^3 then the degree of this term is 3. Since we have an exponent of 3 for the only variable that's in the term x. Another way we can say this is that, this is a third degree term. Now, if, in contrast, we have a term like 6y^7 z^4,, the degree is 11. Or, we could also say, this is an eleventh degree term. Now the degree is 11 here, because, for our first variable we see, we have a power of power of 4. y and z are the only two variables in this expression, so the degree is equal to the sum of their powers. 7 + 4 = 11.

## Polynomial Degree

Just as we can talk about the degree of a term, we can also talk about the degree of an entire polynomial. The degree of a polynomial is just equal to the highest degree of any of its terms. So to figure out the degree of a polynomial we first need to figure out the degree of each of its terms just like we did in the last quiz. If we look back at one of the polynomials we used earlier. -12x^7+3x^2+64x, we can see that this is a by first calculating the degree of each term, so this one is a seventh degree term. This is a second degree term, and this is a first degree term, because of the invisible 1 next to this x that stands on its own. The highest number out of 7, 2 and 1 is 7, so this is a 7th degree polynomial.

## Polynomial Degree ID

Considering this definition of the degree of a polynomial that we just discussed. What is the degree of each of these polynomials down here? Please fill in your answer in the box to the right of each expression

## Polynomial Degree ID

Let's go through these one by one. So first x^3+6y^2. We want to start by finding the degree of each term. So the degree of this first one is 3 and the second term is 2, since we have exponents of 3 and 2 respectively. 3 is greater than 2 so this is a third degree polynomial. Next 7-3x+8x^3y, we have degrees of 0, 1 and 4. Since we have numbers. So this polynomial is of degree last two polynomials as well. One interesting thing to note is that the degree of a polynomial is usually information that comes from just one term in the expression. The term with the highest degree. But in some cases, like in this last example, you might have more than one term that's of the same degree. So for example here we have x^2 which is a second degree term and z^2 which is also a second degree term. Having two terms of this same degree Doesn't change what the highest degree we see here is. We just happen to see that highest degree twice. We still follow the typical rule and say that this is a polynomial of degree two.

## Standard Form

So far when we've seen polynomials, the terms haven't written in any particular order. Remember, we learned before about the commutative property of addition. Changing the order that you add terms together in has no affect on the value of the expression, a+b is just equal to b+a. So any set of terms that you have added together can be written together in any order. And we'll still be mathematically correct regardless of which of those orders you choose to use. However, there is a convention that people use in algebra to help them figure out what order to write the terms of the polynomial in. It's pretty simple. The tendency is to write terms from highest degree to lowest degree. So, for example, if we have this polynomial y+6xy-y^3, we can first figure out the degree of each term and then rearrange these terms so that the degree with the highest degree comes first, and then the rest of the terms continue in descending order of degree. A polynomial written in this way is said to be written in standard form. So again, writing a polynomial in standard form doesn't make it any more mathematically correct than writing the terms in any other order. But mathematicians usually find the standard form a bit more, visually appealing, and it also can help us understand the polynomial as a whole a bit more quickly than we could if we wrote the terms in a different order. Since in standard form, the term with the highest degree comes first, we only need to look at that first term to figure out what the degree of the entire polynomial is. So that's why standard form is particularly convenient.

## Rewriting

Please write these two polynomials in the standard form. If you need to peek, the definition of standard form is right here on the top right-hand corner, but try to do it without looking up here.

## Rewriting

Let's start by finding the degree of each term in either polynomial. I'll go ahead and do that right now. Once we figure out the degree of each term in either expression, we rearrange those terms that the term at the highest degree comes first, and then the rest of the terms go in order of decreasing degree. So for this top polynomial, we'll need the terms to go in order of degree from 3 to 2 to 1 to 0. So that's going to give us We can do the same thing for the second polynomial. Written in standard form, this polynomial is -12x^7+3x^2+64x. Now that we have them written in this way, we can see right off the bat that this top polynomial is a third degree polynomial and this bottom one is a seventh degree one. So standard form definitely makes our job easier. Under that standard form is something that applies to all polynomials not just ones with single variables or ones with just x's. You'll get more practice with other polynomials in standard form later.

## Exponent Notation

So basically exponents give us a convenient notation for showing repeated multiplication of a given number or variable or a combination of numbers and variables. So knowing that, how would you write 7777 using exponent notation? So I know that you can evaluate this expression to equal just a number without any exponent, but for right now I want you to make sure that you use exponent notation for this question.

## Exponent Notation

So, since seven is the number that we're multiplying by itself over and over again, it is the base number. And it goes here as the big number that we write first. Now we have four of these sevens multiplied together so the exponent that we want is four. So that means that 77 77=7^4. Now there are several different ways of saying this answer out loud. You can say seven to the fourth power Seven to the four, seven to the power of four, or just seven to the fourth. Certain other exponents have special names that we use, but they're pretty self-explanatory. For example, 77=7^2, but instead of saying that, we might also say seven squared right here. In the same way, if we have three sevens multiplied together, 777 we get 7^3. But sometimes we say seven cubed instead.

## xxxx

This time, we have xxxxxx. That's a lot of x's to write down. So, what's a different way that you could rewrite this term using exponent notation? Please just use one number or variable in the base, and one number or variable in the exponent. Remember that on a computer, you need to write the base number and then a caret sign and then the exponent number.

## xxxx

X is the thing that we're multiplying by itself, so it is the base. And then, there are six of them multiplied together, so that is the exponent number. Again, the way that you needed to write this on the computer was x^6. This shows that 6 is being shifted up into the exponent slot.

## Exponent Practice

So now I'm going to give you a break and let you actually write just a number as an answer to a quiz. What number, not written in exponent notation or anything, is -3, that quantity to the 4th power equal to?

## Exponent Practice

Since we have parentheses around the negative three here, and the exponent, the four is written outside of those parentheses, that means that the exponent applies to the entire quantity that's inside the parentheses. So, the number that counts as the base number is negative three. Negative three is the thing that we want to multiply by itself four times. So that means we can rewrite this as -3-3-3-3. Now we can just evaluate that numerically. -3-3 is just positive nine, so we get positive nine multiplied by itself, which is just equal to 81. So our final answer is 81.

## No Parentheses

Now if instead I have -3^4, what number does that equal? Is this any different from the quiz before this one?

## Order of Operations Practice

To make sure that you're super solid on order of operations and evaluating expressions using exponents. He'res a kind of fun quiz for you. Please decide whether each of these expressions, is equal to 8, -8, or something else, neither of those 2. Pick the circle, and the proper column for each row.

## Order of Operations Practice

So again, in order to figure out how to evaluate each of these expressions, we need to use our order of operations knowledge. We need to remember our PEMDAS. For this first problem, -2^3, we don't have any parenthess, so that means we need to take the exponent into account before the negative sign. So, we have -12^3, which is the same as -18, so we get negative eight. The next problem has some parentheses in it, so we need to deal with what's inside of those first, and inside, we have -2^2. Just like in this first problem, we need to do the exponent before the negative sign. So, what's inside the parentheses here is negative four since we have -2^2, which is negative four. So this equals For the third problem, we have an exponent outside of something that's inside parentheses. So we know the negative sign is going to be part of the number that is taken to the exponent. So the entire quantity, negative two is squared. So this is equal to 2-2-2, which is the same as have a negative sign inside the parentheses, so its part of this number that's taken to the third power. So -2-2-2 is negative eight. Here, the negative sign comes outside the parentheses, so we have -12^3, to the third is eight and -18 is negative eight. Our last two problems both fall into the neither category, 2+2^2 is just equal to either eight or negative eight. And here, we have -2^2+2^2. Since there is not a parentheses around this negative two we know that we need to square two before multiplying it by negative one. So this is actually equal to -4+4 and that's equal to zero. Great job. I know this is a lot to do in one quiz, but I think that having to think through all of these different options that are sort of similar to each other can be a really good way to make sure you have your order of operations cemented. And if you don't, not a big deal at all. Remember, just go back and practice a little bit more.

## Find the Exponent

Just to change things up a little bit, what if we have 3^2 times 3^4? That's going to equal three to some power, but what is the exponent that should go here?

## Find the Exponent

Let's start by expanding out each of the things that we have with an exponent. So, we know that 3^2 is just equal to 2 threes multiplied together, so 3 times 3. And we know that these two things are also multiplied together, so we need a multiplication sign between these two threes and these four threes. So, again, we just have a bunch of threes multiplied together and, as we know, exponents are just a tool for writing repeated multiplication of the same number in a shorthand way. So our base is going to be three since three is being multiplied over and over again, and we have six of them multiplied together if you count them out. So the exponent is six. Remember, typed in, you need to type 3^6.

## Multiplying Exponents

So, what we saw in this last quiz was really interesting. Remember that we started out with 3^2 times 3^4, and we ended up with 3^6 power. What we need to notice here is how the exponents are related to each other. 2+4, our two original exponents, is equal to 6, the final exponent. So, this actually shows us a general rule for multiplying factors that have exponents. If the two numbers are multiplying together have the same base, then their exponents just add to one another, and the base stays the same. So, let's write that in a more general way. If we have some number, or variable a, and it's taken to the power of b, and that's multiplied by another number a that's taken to the power c. Then together, that multiplication can be written as a^b+c. So, like we saw in the last quiz, in the end. Since exponents indicate repeated multiplication, since each of these factors right here is just the number or variable a being multiplied by itself over and over again some number of times. When they are multiplied together, it's just even more a's multiplied together, or some different number of a's multiplied together. This is just a convenient way for us to not have to write out all of the numbers like we did when we were doing this last quiz.

## Sum of Exponents

Remember that x^2 is just x x or two xs multiplied together. X^4 to the fourth is just 4 xs multiplied together. And we're also multiplying all of that, by another 3 xs that are multiplied together. So here we have a big string of Xs all multiplied together, just like we would expect considering how many exponents we see here, but the same base over and over again. So, in total here, we have 9 ex's multiplied all together.And we know that this just equals x^9. However, we can use our rule to do this in a much shorter and easier way. We can get the same answer by just adding these three exponents together. We know that our base is still x, but our power is just 2 + 4 + answer.

## Different Bases

So what if we have the term x^53^2y^3x^8? How would you simplify that? Please write your answer in a simplified form as you can.

## Different Bases

Let's first rewrite the factors within this term so that the factors with the same bases are next to each other, and I'm also going to put the constant factor first. So I'm going to start with 3^2, then we have two factors that have a base of x. So I'll put those next to each other and the last thing we have is the y cubed. Well we know that 3 ^2 is just 3 3 and 3 3 is just 9. We also know that we have x ^5 x ^8 That's the same as x ^5 + 8 power. And, nothing is being involved with the y cubed so it's just going to stay the same. You'll notice I got rid of those multiplication signs between the different factors in the term since they're implied if we just don't write them. Now the only thing you need to simplify here is add together the two numbers in the exponent of the x. So we get a final answer of 9 x^13 y^3 I think that you are going to find all this practice of manipulating exponents really useful as we keep simplifying expressions

## More Exponent Practice

How would you handle this term y^4 x^2 y^-2? Remember, all these are multiplied together. Please write the most simplified version of this term that you can right here.

## More Exponent Practice

To solve this problem, we can, once again, use this trick that we learned earlier. We have two factors inside this term that have the same base. So, we have y^4 and y^-2. So, I'm going to start by writing those next to each other. And now, we know that y^4 times y^-2, is just going to be equal to y^4+-2. So, I rewrite the x^2 factor and we have y^4+-2, which is the same as 4- 2power. y^2.

## Negative Exponents

So remember at the, in the last quiz, we simplified h^4 x^2 y^-2 to equal x^2 y^2. But in doing this, we actually dealt with something we haven't talked about explicitly before. This negative exponent right here. My question for you now is basically, what do negative exponents mean? So, which of these five answers down here is an equivalent expression to what we started out with, y^4x^2y^-2.  Remember, whatever you pick down here also needs to give us the final answer of x^2 y^2 in the end. So, think about what intermediate step you need between here and here and which one of these answer choices fits that. This is definitely a little bit tricky so good luck.

## Negative Exponents

As we saw in the quiz before this one, when we multiplied y^4 times y^-2, we used our short cut to say that this is just equal to, of course, leaving the x^2 there, y^4-2 power. The role that this -2 exponent here plays then, is that it makes it so that, in the final answer, which we know is x^2y^2, we have two fewer y's multiplied together than we did in at least this first part, the y^4 factor of the original expression. But how do you write y^-2 in terms of multiplying some number of y's together. Well if we know that y^4xy^-2=y^2. And also, we remember that y^4 is four ys multiplied together. And similarly, y^2 is two ys multiplied together. This y^ -2 needs to cancel out two of these other four ys that are multiplied together, to give us our final answer. Now, we know that the way that we undo multiplication is division. y^4 needs to be divided by y^2, to equal y squared, we can write this out like this. We have four y's multiplied together, divided by 2 y's multiplied together, and each of these y's in the denominator cancels out one of the y's in the numerator, since everything here is just multiplied together. This is how we end up with just two y's multiplied together. Together, since we can see that we only have y times y left on the left side. If we just look at this way of writing our expression though, we can write both the numerator and the denominator in terms of exponents. So, on the top, we still have y^4 and the bottom of our fraction we have y times y, which is just y^2. So, if we move this way where an expression appear to be end up with y^4 times y^-2=y^4/y^2. We see this factor may be not we so need to multiply this pair x ^ 2 to get a final answer. In this answer choice right here, y^4x^2/y^2.

## Up or Down

So, what we learned from the last quiz is that, when you have a negative exponent, you can rewrite whatever term you're dealing with, so that we're instead, dividing by that factor inside the term. So, negative exponents are actually veiled ways of writing division into our term. The way we know what we're dividing by, is to find the factor with a negative exponent, which is just y^-2, in this case. And we move it underneath the factors of the positive exponents to make it the denominator of the term. So, on the right side of the equation where we've moved it, it's now in the denominator. And we've also changed the power of the base to be positive instead of negative. So, we flip the sign of an exponent from negative to positive or from positive to negative. We need to move the factor or the base number that the exponent is applied to, to the opposite side of the fraction. If it's in the top, it needs to move to the bottom and if it's in the bottom, it needs to move to the top, and we also flip the sign of the exponent. So here, we change from negative to positive. So basically, if we have some number, let's call it x and it's taken to a negative power, let's say, that's -a, where a could be any number, or really any expression. Then, this is equal to 1/x^a. So again, we multiply the exponent of a number by -1. We need to switch which part of the fraction the factor it belongs to is part of. I know that what's on the left side here doesn't look like a fraction, but this is actually secretly x^-a/1. So, anything that doesn't look like it's part of a fraction is actually in the numerator of your fraction, where the denominator is 1.

## No Negative Exponents

Using what you just learned about signs of exponents and how that relates to the side of the fraction they're on, how could you rewrite 3y-1 x3 in fraction notation? So, just fill in what you think belongs in the numerator here and what belong in the denominator here. There are a bunch of different mathematically equivalent ways of doing this, but I want you to do it in a way so that you have something that's equal to this expression but so that there are no negative exponents in either the numerator or the denominator over here.

## No Negative Exponents

We know that this exponent of -1, attached to the base of y here, means that we can rewrite this factor, y^-1 as 1 / y^1. And we know that y^1 is just y. So y^-1 = of y^-1 in this term. So now, we have All of these factors are just multiplied together, so we can write our fraction right away. In the numerator, we have 3 and x^3. And, the only thing written in the denominator is the y. So, our final answer is 3x^3 / y.

## No Negative Exponents 2

So here's a quiz that looks pretty similar to the last one we did. How can you rewrite 3m ^ 2 / n ^ -4 so that it contains no negative exponents?

## No Negative Exponents 2

What I'm going to do first to deal with this negative exponent factor is separate it out from the rest of the factors. So I'm just going to multiply a little bit more explicitly. So you have 3m^21/n^-4. However, we know that when we have a negative exponent, n^4 in our case, these factors actually equal to 1/n^4. So I need to replace just the denominator of this fraction right here with this number. So that's going to give us This is really not looking very pretty. However, we know how to handle this. Dividing by a fraction is the same as multiplying by its reciprocal. So, for example, we have 1/a/b. That's just equal to 1b/a. So we can continue modifying this expression using that trick. This is going to equal, keeping the 3m^2, we keep the numerator here, and we multiply by the reciprocal of the denominator. So the reciprocal of 1/n^4 is just n^4/1. Well now this is easy. You know that anything times 1 is just itself. And we know anything divided by 1 is just itself. So this leaves us with 3m^2n^4. So again, we see that switching the sign of an exponent, so switching from negative the n base. Just requires a flipping of the exponent sign and a flipping of the side of the equation that factors on. We switch from having n^-4 in the denominator to having n^4 in the numerator. If you found working with fractions like this a little bit difficult, not a big deal at all. Just take some time to review manipulation of fractions with the materials that we've directed you to.