Question

If $\sin 5\theta =\cos 4\theta$, where $5\theta$ and $4\theta$ are acute angles, then the value of $\theta$ is

• A. 15
• B. 8
• C. 10
• D. 12

Answer 1

The correct option is C 10

Given, $\sin 5\theta =\cos 4\theta$
$\Rightarrow \cos ({90}^0-5\theta )=\cos 4\theta$
$\Rightarrow {90}^0-5\theta =4\theta$
$\Rightarrow 9\theta ={90}^0$
$\Rightarrow \theta ={10}^0$