I really don't have a favorite theorem, because there are some many awesome theorems out there. However, I like the Side-Angle-Side (SAS) Theorem in geometry that says if two triangles have two sides equal, and the included angle equal, then the two triangles are congruent. This means that all corresponding sides and angles are equal!
For a visual example of the SAS Theorem and to test your knowledge of the SAS Theorem, go here!
