This document discusses applying properties of similar triangles to find unknown segment lengths. It begins with examples showing how to use the triangle proportionality theorem and triangle angle bisector theorem to find missing side lengths. An example application involves an artist's sketch and finding lengths based on similar right triangles. The lesson concludes with a quiz to practice applying the concepts. The key ideas covered are using proportions set up with the cross product property to find unknowns, and applying theorems about similar triangles to verify or determine parallelism or lengths of segments.