180 Rule for Triangles

180 Triangle Rule Problems

The 180 rule sounds simple: the angles of a triangle always add up to 180 degrees. And it is simple, until they start throwing in x's, and 2x's, and 180-2x's... You get the idea.

Triangle Exterior Angle Theorem

This is one of those things you have to learn "just because". You won't see it again, you may not even see it on the test, yet it will be on your homework and you'll waste time studying it because you think it might be on the test. Oh well, at least you can do these problems with the 180 rule instead!

180 Rule & Exterior Angle Theorem Proofs

Proofs are so awesome. In this video we prove the Triangle Exterior Angle Theorem, which is probably on your homework assignment.