Question

Find the missing piece to make this equal on both sides

sin pi/4 sin pi/6 = 1/2( cos pi/12 - _?__ 5pi/12)

Answer 1

The rule to solve this problem:
sin x sin y = 0.5 [ cos (x-y) - cos (x+y) ]

∴ If x = π/4 and y = π/6
x-y = π/12 and x+y = 5π/12

∴ sin (π/4) sin (π/6) = 0.5 [ cos (π/12) - cos (5π/12) ]