\[\begin{array}{l}
d)\,\,\left( {1 + 2\cos x} \right)\left( {3 - \cos x} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
1 + 2\cos x = 0\\
3 - \cos x = 0\,\,\,\,\left( {VN} \right)
\end{array} \right.\\
\Leftrightarrow \cos x = - \frac{1}{2}\\
\Leftrightarrow \left[ \begin{array}{l}
x = \frac{{2\pi }}{3} + k2\pi \\
x = - \frac{{2\pi }}{3} + k2\pi
\end{array} \right.\,\,\,\left( {k \in Z} \right).
\end{array}\]
