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

Introduction

Learn what triangles are and how they are classified.

1. Types of Triangles
2. Triangles (Basics)

Interior Angles

Understand the interior-angle sum of a triangle and practice finding missing angles.

1. Sum of Angles of a Triangle is 180° (Proof)
2. Find the Missing Angle of a Triangle

Exterior Angles

1. Sum of Exterior Angles of a Triangle (Proof)
2. Exterior Angle Theorem of a Triangle
3. Two Exterior Angles at a Vertex are Equal (Proof)
4. Two Exterior Angles are Equal at a Vertex (Quick Proof)

🔗 Related Topic

• Pythagorean Theorem (Right Triangle Special Case)

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