Description: Sal explains why the slope between any two points on a given line is constant using similar triangles. We tend to be told in algebra class that if we have a line, our line will have a constant rate of change of y with respect to x. And our slope is literally defined as your change in y, this triangle is the Greek letter delta. What I want to do in this video is to actually prove that using similar triangles from geometry.*Teacher Advisor is 100% free.