DEPRECATED Understanding angle addition formulas

Problem

Prove the sine angle-sum identity by labeling lengths and angles in this diagram.
Some of the proof has been done for you in pink.
Segment/Angle
Measure
  • start overline, B, C, end overline
  • angle, C, B, D
  • angle, D, C, B
  • start overline, C, D, end overline
  • start overline, C, E, end overline
  • sine, y
  • cosine, y, sine, x, plus, sine, y, cosine, x
  • x
  • sine, y, cosine, x
  • start fraction, pi, divided by, 2, end fraction, minus, x
Do 4 problems