Khan Academy on a Stick

Congruence postulates

We begin to seriously channel Euclid in this tutorial to really, really (no, really) prove things--in particular, that triangles are congruents. You'll appreciate (and love) what rigorous proofs are. It will sharpen your mind and make you a better friend, relative and citizen (and make you more popular in general). Don't have too much fun.

Congruence and isosceles and equilateral triangles

This tutorial uses our understanding of congruence postulates to prove some neat properties of isosceles and equilateral triangles.