Use Similar Triangles

This video introduces the concept of using similar triangles to find missing side lengths. Similar triangles share the same shape but have different sizes. These triangles have all equal angle measures but the side lengths are usually different.

The example problems will show two or more triangles that may be similar and the goal is to find a missing side length on one of the triangles. The corresponding side lengths in these triangles are proportional. The smaller triangle is a scaled version of the larger triangle and vice versa. Going from the smaller triangle to the larger, each side length is multiplied by the same number or proportionality constant.

The general strategy is to set up an equation showing the proportionality of the corresponding side lengths to find the missing side of the triangle.

Khan Academy exercise to practice: