Question

Sin 3A = cos (A – 70ᵒ), where A is an acute angle then
A = ________________ ᵒ.

Answer 1

A = 40°

Explanation:

`\sin 3A = \cos (A – 70ᵒ) \\ \\ \cos(90 \degree - 3A) = \cos (A – 70ᵒ) \\ \{\because \: \cos(90 \degree - \theta) = \sin \theta \} \\ \\ (90 \degree - 3A) = (A – 70ᵒ) \\ \\ 90 \degree + 70ᵒ = 3A + A \\ \\ 160 \degree = 4A \\ \\ A = (160 \degree)/(4) \\ \\ \huge \red{ \boxed{A = 40 \degree}}`