$\Leftrightarrow\left[\begin{array}{I} x=3k\pi\\x=\pm\frac{\pi}{2}+k3\pi\\x=\pm\frac{5\pi}{4}+k3\pi\end{array}\right.$Kết hợp ĐK $\cos 2x>0\Rightarrow x=3k\pi, k\in Z$
Thẻ
Lượt xem