Geometry - 2D

Alternate Exterior Angles: http://www.youtube.com/watch?v=PuWdjqikkDM&feature=plcp

Alternate Interior Angles: http://www.youtube.com/watch?v=HDdNywDR9Cg&feature=plcp

Angles and Degrees: https://www.youtube.com/watch?v=_n3KZR1DSEo

Classifying Triangles by Angle: http://www.youtube.com/watch?v=XXPi2Nv0Z8A

Classifying Triangles by Side: http://www.youtube.com/watch?v=kepsp-97qUI

Classifying Polygons (Advanced): http://www.youtube.com/watch?v=_01VVaulMME

Complementary Angles: http://www.youtube.com/watch?v=_pLuFkskhqY&feature=plcp

Pythagorean Theorem: http://www.youtube.com/watch?v=oflTCDskvTM&feature=plcp

Quadrilateral Family Tree: http://www.youtube.com/watch?v=xYKefVhW1Z8&feature=plcp

Sum of Angles in Polygons: http://www.youtube.com/watch?v=GLZGAuuj9NY&feature=plcp