Question

Solve for 0. Sin 75° = cos 0

Answer 1

Cosine means complementary sine, the sine of an angle and the cosine of the  complementary angle are the same.

sin 75° = cos θ

cos (90° - 75°) = cos θ

cos 15° = cos θ

In general when we have

cos x = cos a

the solution is

x = ±a + 360°k, integer k

Here they just went with x=a, or

θ = 15°

Answer: C      θ = 15°