Question

If sin 21 = cos (5x+9) what is the value of x

Answer 1

sin x = cos 54 = sin (90-54) = sin 46

Hence x = 46 deg

Same technique. Sin 21 = cos (5x+9) = sin (90-5x-9)

81-5x = 21

Or 5x = 60

Or x = 12 deg

hope it helps