Evaluate the following expressions. Your answer must be an exact angle in radians and in the interval [0,π]\displaystyle {\left[{0},\pi\right]}. Example: Enter pi/6 for π6\displaystyle \frac{\pi}{{6}}.

(a) cos⁡−1(−1)=\displaystyle {{\cos}^{{-{1}}}{\left(-{1}\right)}}=  

(b) cos⁡−1(−32)=\displaystyle {{\cos}^{{-{1}}}{\left(-{\frac{{\sqrt{{{3}}}}}{{{2}}}}\right)}}=  

(c) cos⁡−1(12)=\displaystyle {{\cos}^{{-{1}}}{\left({\frac{{{1}}}{{{2}}}}\right)}}=  

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