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Khan Academy
Khan Academy: Geometry: Proof Sum of Measures of Angles in a Triangle Are 180
Proof that the sum of the angles in a triangle is 180 using the relationship of angles formed when parallel lines are cut by a transversal. This video also appears in the Geometry: Triangles strand. [6:31]
Khan Academy
Khan Academy: Triangles: Proof Sum of Measures of Angles in a Triangle Are 180
Video proving that the sum of the measures of the angles in a triangle are 180.