Glossary for Lesson 5-3: Midpoint


The midpoint of a line segment connecting two points (the endpoints of the segment) is the point on that segment that is an equal distance away from the two endpoints.  The coordinates of the midpoint of the segment connecting (x_1, y_1) and (x_2, y_2) can be found according to the midpoint formula : (\frac {(x_1+x_2)}{2}, \frac {(y_1+y_2)}{2}) The x -coordinate of the midpoint is the average of the x -coordinates of the endpoints, and the y -coordinate of the midpoint is the average of the y -coordinates of the endpoints.


A quadrilateral is a two-dimensional figure with four sides.  Examples include rectangles, rhombuses, squares, and trapezoids.


The slope of a line is a number that tells us how steep the line is.  We can find this number by calculating how many units the line rises vertically for every unit it moves to the right or to the left.  This is sometimes referred to as “rise over run”.  Two find the slope of the line on which the points (x_1, y_1) and (x_2, y_2) lie, we can use the following formula, in which m represents the slope: m=\frac {y_2-y_1}{x_2-x_1}

Parallel Lines

Two lines are called parallel if their slopes are equal.  Parallel lines that are not identical will never intersect one another.  The symbol || is sometimes used to show that two lines are parallel to one another.