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Phương trình tương đương với:
$\sqrt2 \sin(2x+\frac{\pi}{4})=\sqrt2 \sin3x$
$\Leftrightarrow \sin(2x+\frac{\pi}{4})=\sin3x $
$\Leftrightarrow \left [ \begin{array}{l} 2x+\frac{\pi}{4}=3x+2k\pi\\2x+\frac{\pi}{4}=\pi-3x+2k\pi \end{array} \right. (k\in\mathbb{Z})$
$\Leftrightarrow \left[ \begin{array}{l} x=\frac{\pi}{4}-2k\pi\\x=\frac{3\pi}{20}+\frac{2k}{5}\pi \end{array} \right. (k\in\mathbb{Z})$
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