Evaluate each of the following:

(i)`cos^(-1)(cos((13pi)/6))`

(ii) `cos^(-1)(cos3)`

(iii) `cos^(-1)(cos4)`

Explanation

(i) Let y=`\cos ^{-1}(\cos \frac{13 \pi}{6})`


`\cos y=\cos \frac{13 \pi}{6}`

`\cos y=\cos (390^{\circ})`


But, Range of `\cos ^{-1} is [0, \pi]`

i.e. `[0^{\circ}, 180^{\circ}]`

Hence, `y=390^{\circ}` not possible

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