Learn triangle basics, angle facts, and key theorems with proofs and examples.

Lessons

1. Types of Triangles
2. Triangles (Basics)
3. Sum of Angles of a Triangle is 180° (Proof)
4. Find the Missing Angle of a Triangle (Examples)
5. Sum of Exterior Angles of a Triangle (Proof)
6. Exterior Angle Theorem of a Triangle (Examples)
7. Two Exterior Angles at a Vertex are Equal (Proof)
8. Why Two Exterior Angles are Equal at a Vertex (Quick Proof)