MCQ
${\cos ^{ - 1}}\left( {\cos \frac{{7\pi }}{6}} \right) = .....$
- A$\frac{\pi }{6}$
- ✓$\frac{{5\pi }}{6}$
- C$ - \frac{\pi }{6}$
- D$\frac{{7\pi }}{6}$
${\cos ^{ - 1}}\left( {\cos \frac{{7\pi }}{6}} \right) = {\cos ^{ - 1}}\left[ {\cos \left( {\pi + \frac{\pi }{6}} \right)} \right]$
$ = {\cos ^{ - 1}}\left( { - \cos \frac{\pi }{6}} \right)$
$ = \pi - {\cos ^{ - 1}}\left( {\cos \frac{\pi }{6}} \right)$
$ = \pi - \frac{\pi }{6} = \frac{{5\pi }}{6}$
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