Question

$\cos (-{435}^{\circ })=$

• A. $\cos {15}^{\circ }$
• B. $-\cos {15}^{\circ }$
• C. $-\sin {15}^{\circ }$
• D. $\sin {15}^{\circ }$

Answer 1

The correct option is D $\sin {15}^{\circ }$

Since, $\cos (-x)=\cos x$
$\Rightarrow \cos (-{435}^{\circ })=\cos \left({435}^{\circ }\right)$
$=\cos ({360}^{\circ }+{75}^{\circ })$
$=\cos \left({75}^{\circ }\right)$
$=\cos ({90}^{\circ }-{15}^{\circ })$
$=\sin {15}^{\circ }$
Option $D$ is correct.