G.GSR.4.5
Use geometric reasoning to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles.
Khan Academy ResourcesProve theorems using similarityProve triangle propertiesLine and angle proofsProofs with transformationsAngles in a triangle sum to 180° proofTriangle exterior angle exampleProofs concerning isosceles trianglesProofs concerning equilateral trianglesExploring medial trianglesProving triangle medians intersect at a pointProofs with transformations

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