Triangle

A triangle is a polygon with three sides.

Introductory topics

• Congruence
• Similarity
• Triangle inequality
• Area
• Angle bisectors
• Incircle
• Circumcircle
• Centroid

Resources

Books

• Introduction to Geometry by Richard Rusczyk

Intermediate topics

• Geometric inequalities

Resources

Books

• Challenging Problems in Geometry -- A good book for students who already have a solid handle on elementary geometry.
• Geometry Revisited -- A classic.