# Glossary for Lesson 15: Quadratic Formula

### Plus or Minus (\pm)

The plus or minus sign \pm is used to indicate that the value to its can be either added or subtracted to the value to its left.  For example, 8\pm 3 is a way of writing 8+3 or 8-3 using just one expression.  To write this symbol with MathQuill, type \pm and then a space.

The quadratic formula is a formula that can be used to find solutions to quadratic equations.  If a quadratic equation is written in the form ax^2+bx+c=0 , then the quadratic formula states that its solutions will be: x=\frac {-b\pm \sqrt{b^2-4ac}}{2a}

### Root or Zero

A root of a polynomial, also called a zero of a polynomial, is a value of x that makes the polynomial equal to 0.  For a polynomial equation, if a root is a real number, then this tells us the x-coordinate of one of the graphs’ x-intercepts.  Solutions to the quadratic formula, for example, tell us the roots of quadratic equations. Let’s say that we have the equation y=x^2+4x+3.  We can factor this to be y=(x+3)(x+1) .  If we set y=0 , then the values that solve the quadratic equation 0=(x+3)(x+1) are the roots of the polynomial equation, x=-3 and x=-1