If sin 3A = cos (A – 10°) and ∠ A is acute then ∠ A = ?

Question

Philoid · Accepted Answer

We are given that: sin 3A = cos (A – 10°)

∴ We can rewrite it as: cos (90° – 3A) = cos (A – 10°)

On comparing both sides, we get,

90° – 3A = A – 10°

⇒ A + 3A = 90° + 10°

⇒ 4A = 100°

⇒ A = 25°