Question

If cos x = sin(20 + x)° and 0° < x < 90°, the value of x is
°.

Answer 1

cos x = sin(20 + x)

sin(90-x) = sin(20+x)

=> 90-x = 20+x => 2x = 70 => x = 35

We need only x ∈ (0,90) so this is the only answer.