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

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

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

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