In this video, learn how similar triangles can be used to help explain the concept of slope. In the accompanying classroom activity, students apply the concept of similar triangles to explore the slope between different points on the coordinate plane. Students may already know that two points make a line. In the activity, they use similar right triangles to explore why the slope of a line is constant between any two points on that line. The activity begins with a review of two concepts: similar triangles and slope. Students then watch the video, which relating the two ideas, and break into partner groups to develop mathematical arguments relating slope and similarity.