\(\begin{array}{l}
\cos x = 1 \Leftrightarrow x = k2\pi \,\,\,\left( {k \in Z} \right)\\
\cos x = 0 \Leftrightarrow x = \frac{\pi }{2} + k\pi \,\,\left( {k \in Z} \right)\\
\cos x = - 1 \Leftrightarrow x = \pi + k2\pi \,\,\left( {k \in Z} \right)
\end{array}\)