MCQ
The value of $\sin^{-1}\Big(\cos\frac{33\pi}{5}\Big)$ is:
  • A
    $\frac{33}{5}$
  • $-\frac{\pi}{10}$
  • C
    $\frac{\pi}{10}$
  • D
    $\frac{7\pi}{5}$

Answer

Correct option: B.
$-\frac{\pi}{10}$
$\sin^{-1}\Big(\cos\frac{33\pi}{5}\Big)$
$=\sin^{-1}\Big(\cos\Big(6\pi+\frac{3\pi}{5}\Big)\Big)$
$=\sin^{-1}\Big(\cos\Big(\frac{3\pi}{5}\Big)\Big)$
$=\sin^{-1}\Big(\sin\Big(\frac{\pi}{2}-\frac{3\pi}{5}\Big)\Big)$
$=\frac{\pi}{2}-\frac{3\pi}{5}$
$=\frac{-\pi}{10}$

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