Question

cos-1bracket cos13paai upon 6 bracket close

Answer 1

$\cos{ }^{ - 1} (\cos( \frac{13\pi}{6} )) \\ = \cos^{ - 1} ( \cos(2\pi + \frac{\pi}{6} ) ) \\ = \cos {}^{ - 1}( \cos( \frac{\pi}{6} ) ) \\ = \frac{\pi}{6}$
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Answer 2

cos−1(cos(613π​))=cos−1(cos(2π+6π​))=cos−1(cos(6π​))=6π​