US Common Core State Standard Math 8.G.A.5
Demonstrations 1 - 8 of 8

Description of Standard: Use informal arguments 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. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.

 Interior and Exterior Angles of Regular Polygons The Interior Angles of a Triangle Sum to Pi A Line Crossing Two Parallel Lines Makes Alternate Angles Equal Eratosthenes's Measure of the Earth's Circumference Sum of Exterior Angles of a Polygon Einstein's Most Excellent Proof Oriented Triangle Angles Parallel Lines: Angles with a Transversal

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