Parallel lines, transversal lines, corresponding angles
Parallel lines 1 is a free educational video by Khan Academy.It helps students in grades 8 practice the following standards 8.G.A.5.
1. 8.G.A.5 : 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 three angles appear to form a line, and give an argument in terms of transversals why this is so..