Trong các mệnh đề sau, mệnh đề nào đúng?

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

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

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

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