2 câu trả lời
$2\sin2x= -1$ $\Rightarrow \sin 2x=\dfrac{-1}{2}=\sin(\dfrac{-\pi}{6})$ $\Rightarrow \left[ \begin{array}{l} 2x=\dfrac{-\pi}{6}+k2\pi \\ 2x=\pi-\dfrac{-\pi}{6}+k2\pi\end{array} \right .$ $\Rightarrow \left[ \begin{array}{l} x=\dfrac{-\pi}{12}+k\pi \\ 2x=\dfrac{7\pi}{12}+k\pi\end{array} \right .(k\in\mathbb Z)$
Đáp án:
2sin2x= -1;
<=> sin2x=$\frac{-1}{2}$ ;
<=> sin2x=sin $\frac{-\pi}{6}$;
<=>$\left \{ {{2x=\frac{\pi }{6}+k2\pi } \atop {2x=\frac{5\pi }{6}+k2\pi }} \right.$ ;
<=> $\left \{ {{x=\frac{\pi }{12}+k\pi } \atop {x=\frac{5\pi }{12}+k\pi }} \right.$
Giải thích các bước giải:
