Find the exact value of each expression

Question

1. sin(3pi/4)sin(pi/12)
2. -5(sin(11pi/12)-sin(7pi/12))

Answer 1

sin π/12 = sin (π/3 - π/4)

sin 11π/12 = sin (3π/12 + 8π/12)

sin 7π/12 = sin (3π/12 + 4π/12)

Use sum/difference formulas