172 6_3_3 Formula Review and Geometry Perspective M2U00433.mp4Review and use of the double-angle, power-reducing, and half-angle identities. We then construct a geometric proof that the angle inscribed in a circle subtending the arc is one-half of the central angle. This will help us set up a geometric proof of the half-angle identities. 26m13s © 2008 by Raymond E. Griffith.