If the lengths of two sides of a triangle are multiples of two corresponding sides of another triangle (i.e. they are in proportion), and the included angles are congruent, then the triangles are similar.
Similar Triangles: Determine proportions comparing the side lengths of similar triangles.
Side Splitter: Find a relationship between sides in two triangles.
Altitude to the Hypotenuse: Investigate the relationship between sides of right triangles when an altitude is drawn to the hypotenuse of a right triangle.