Trong các mệnh đề sau, mệnh đề nào đúng?

\(\cos x = \cos \alpha \Leftrightarrow \left[ \begin{array}{l}x = \alpha + k2\pi \\x = - \alpha + k2\pi \end{array} \right.\left( {k \in Z} \right)\).

\(\cos x = \cos \alpha \Leftrightarrow \left[ \begin{array}{l}x = \alpha + k\pi \\x = \pi - \alpha + k2\pi \end{array} \right.\left( {k \in Z} \right)\).

\(\cos x = \cos \alpha \Leftrightarrow \left[ \begin{array}{l}x = \alpha + k\pi \\x = - \alpha + k\pi \end{array} \right.\left( {k \in Z} \right)\).

\(\cos x = \cos \alpha \Leftrightarrow \left[ \begin{array}{l}x = \alpha + k\pi \\x = \pi - \alpha + k\pi \end{array} \right.\left( {k \in Z} \right)\).