\(sin3x=sinx\Rightarrow\left[{}\begin{matrix}3x=x+k2\pi\\3x=\pi-x+k2\pi\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=k\pi\\x=\dfrac{\pi}{4}+\dfrac{k\pi}{2}\end{matrix}\right.\)
Trên \(\left[-\dfrac{\pi}{2};\dfrac{\pi}{2}\right]\) pt có các nghiệm \(-\dfrac{\pi}{4};0;\dfrac{\pi}{4}\)
Đáp án A