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  4. cos -1[ cos ((7 π/5))] is equal to

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Q. $\cos ^{-1}\left[\cos \left(\frac{7 \pi}{5}\right)\right]$ is equal to

KEAMKEAM 2014

Solution:

$ \cos ^{-1}\left(\cos \frac{7 \pi}{5}\right) =\cos ^{-1}\left[\cos \left(2 \pi-\frac{3 \pi}{5}\right)\right] $
$ =\cos ^{-1}\left(\cos \frac{3 \pi}{5}\right)=\frac{3 \pi}{5} $