Proving slope is constant using similarity (Full video)

Khan Academy

Supporting grades: 8

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.

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