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### Course: High school math (India) > Unit 3

Lesson 8: Triangles and quadrilaterals- Angles in a triangle sum to 180° proof
- Triangle exterior angle example
- Angle sum property of a triangle
- Triangle inequality theorem
- Triangle inequality
- Triangle congruence postulates/criteria
- Congruent triangles
- Intro to the Pythagorean theorem
- Pythagoras theorem
- Intro to quadrilateral
- Proof: Diagonals of a parallelogram
- Quadrilateral types
- Sum of interior angles of a polygon
- Quadrilaterals

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