Question

Evaluate sin 7pi/12. Using sum, difference, and cofunction identities

Answer 1

well, 7 = 6 + 1
so it is really

sin (6 pi/12 + pi/12)

sin(a+b) = sin a cos b + cos a sin b
(just like your other problem)
sin 6 pi/12 = sin 90 = 1
cos pi/12 = cos 15 deg

cos 90 = 0

so cos 15 degrees