Question

Write the value of cos⁻¹ (cos 6).

Answer 1

We know that ${\cos }^{-1}\left(\cos x\right)=x$.
Now,
$$\begin{gathered} {\cos }^{-1}\left(\cos 6\right)={\cos }^{-1}\left\{\cos \left(2\mathrm{\pi }-6\right)\right\} \\ =2\mathrm{\pi }-6 \end{gathered}$$