Similar triangles to prove that the slope is constant for a line  Algebra I  Khan Academy  Summary and Q&A
TL;DR
The video demonstrates the proof of constant slope in a line using similar triangles.
Questions & Answers
Q: How is slope defined in algebra?
Slope in algebra is defined as the change in y over the change in x. It represents the rate of change or inclination of a line.
Q: How can similar triangles be used to prove constant slope?
Similar triangles have congruent corresponding angles and the ratio of corresponding sides is constant. By showing that triangles formed by different sets of points on a line are similar, we can demonstrate that the ratio of change in y to change in x (slope) is constant.
Q: What are the characteristics of the triangles used in the proof?
The triangles used in the proof are right triangles, with the green lines representing horizontal segments and the purple lines representing vertical segments. The angles formed by these segments are congruent.
Q: Why is the constant ratio of the change in y to the change in x important?
The constant ratio represents the slope of a line, which quantifies its inclination or rate of change. By proving that this ratio remains the same for any two arbitrary points on the line, it establishes the slope as constant for the entire line.
Summary & Key Takeaways

The video explains that lines have a constant rate of change, inclination, or slope, and the slope is defined as the change in y over the change in x.

The speaker illustrates the concept by considering two sets of points and calculating the change in x and change in y for each set.

Similar triangles are used to prove that the ratio of the change in y to the change in x is the same for different sets of points, establishing the constant slope of a line.