\[\begin{array}{l}
Cos\left( {x + 3} \right) = \frac{1}{3}\\
\Leftrightarrow \left[ \begin{array}{l}
x + 3 = \arccos \frac{1}{3} + k2\pi \\
x + 3 = - \arccos \frac{1}{3} + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \arccos \frac{1}{3} - 3 + k2\pi \\
x = - \arccos \frac{1}{3} - 3 + k2\pi
\end{array} \right.\left( {k \in Z} \right)\\
vay:S = \{ \arccos \frac{1}{3} - 3 + k2\pi ; - \arccos \frac{1}{3} - 3 + k2\pi \} \\
Cos\left( {x - 2} \right) = \frac{2}{5}\\
\Leftrightarrow \left[ \begin{array}{l}
x - 2 = \arccos \frac{2}{5} + k2\pi \\
x - 2 = - \arccos \frac{2}{5} + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \arccos \frac{2}{5} + 2 + k2\pi \\
x = - \arccos \frac{2}{5} + 2 + k2\pi
\end{array} \right.\left( {k \in Z} \right)\\
vay:S = \{ \arccos \frac{2}{5} + 2 + k2\pi ; - \arccos \frac{2}{5} + 2 + k2\pi \}
\end{array}\]