Sum of interior angles of a polygon : Khan Academy on a Stick

Khan Academy on a Stick

Angles with triangles and polygons

Proof: Sum of measures of angles in a triangle are 180
Triangle angle example 1
Triangle angle example 2
Triangle angle example 3
Challenging triangle angle problem
Proof: Corresponding angle equivalence implies parallel lines
Finding more angles
Sum of interior angles of a polygon
Sum of the exterior angles of convex polygon

If the above player doesn't work, try this direct link.