Question

If $\cos ({20}^{\circ }+\theta )=\sin {30}^{\circ }$, then the value of $\theta$ is:

• A. ${20}^0$
• B. ${50}^0$
• C. ${30}^0$
• D. ${40}^0$

Answer 1

Answer: (D)

${40}^0$

$\cos (20°+\theta )=\sin 30°$

$\Rightarrow \sin (90°-20°-\theta )=\sin 30°$

$\Rightarrow 70°-\theta =30°$

$\Rightarrow \theta =40°$