Giải phương trình: \({\sin ^2}2x - 3\cos 2x + 3 = 0\).

\({\sin ^2}2x - 3\cos 2x + 3 = 0\)

\( \Leftrightarrow 1 - {\cos ^2}2x - 3\cos 2x + 3 = 0 \Leftrightarrow - {\cos ^2}2x - 3\cos 2x + 4 = 0\)

\( \Leftrightarrow \left[ {\begin{array}{*{20}{c}}{\cos 2x = 1(TM)}\\{\cos 2x = - 4(L)}\end{array}} \right. \Leftrightarrow 2x = k\pi \left( {k \in \mathbb{Z}} \right) \Leftrightarrow x = \frac{{k\pi }}{2}\left( {k \in \mathbb{Z}} \right)\)