Triangles & Congruence
Classify triangles and prove the 180° angle sum; the exterior-angle theorem and triangle inequality; and the congruence shortcuts SSS, SAS, ASA, AAS, HL with CPCTC and isosceles triangles.
Builds on
Unit 1's angles, Unit 2's proofs, and Unit 3's parallel-line facts — the angle sum is proven straight from alternate interior angles.
Lessons