đề thi toán khối D
Câu 2: $sin3x + cos2x - sinx = 0$
$\Leftrightarrow 2cos2xsinx + cos2x = 0$
$\Leftrightarrow cos2x = 0 \vee sinx = \frac{-1}{2}$
$\Leftrightarrow x=\frac{\pi}{4} + \frac{k\pi}{2} \vee x=-\frac{\pi}{6}+l2\pi \vee x=\frac{7\pi}{6}+m2\pi$
$(k, l, m \in \mathbb{Z})$