If sinA= -5/13 with angle A in quadrant 3, and cosB= -8/17 with angle B in quadrant 2, then find

Question

1. sin (a-b)
2. cos (a+b)

Answer 1

sin a = -5/13 → cos a = -12/13

cos b = -8/17 → sin 15/17

sin (a - b) = cos a cos b - sin a sin b

cos (a + b) = cos a cos b - sin a sin b