If sin 70° = cos x, where x is an acute angle, what is the value of x?
Correct: B
We use the complementary angle identity: sin θ = cos (90° - θ). Comparing sin 70° = cos x with this identity, we can write sin 70° as cos (90° - 70°) = cos 20°. So, cos 20° = cos x. Since x is an acute angle, we can equate the angles: x = 20°.