8.EE.6

8.EE.6  Slopes, Triangles & the coordinate plane  Use similar triangles to explain why the slope m is the same between any two distinct points on a nonvertical line in the coordinate plane; derive the equation y = mx for a line through the origin and the equation y = mx + b for a line intercepting the vertical axis at b.

What this means we are covering (2 main things)


You can "build" a line by using similar right triangles. The hypotenuses, the longest side across from the right angle, can be "linked" together to form a line. And you will notice the slope of the line is a ratio of the legs of the triangles  rise over run.