If sin(x-20°)=cos(3x-10°),find x.

Answer 1

use the fact that
cos Ø = sin (90° - Ø)

cos(3x - 10) = sin(90 - (3x-10) )
cos(3x - 10) = sin(100 - 3x)

so sin(x-20) = sin(100 - 3x)
then:
x-20 = 100-3x
4x = 120
x = 30

check with your calculator