Sine and Cosine of Two Angles
A construction show
cos(A+B) = cos(A)cos(B) - sin(A)sin(B)
sin(A+B) = sin(A)cos(B) + cos(A)sin(B)
All lengths are measured relative to a unit of AC.
The c's and s's are short forms for cos() and sin().
The blue triangles are similar.
Move points A, C and W to show different geometrical arrangements.