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PT
$\Leftrightarrow \sin\left(\dfrac{\pi }{3}-4x\right)+\sin\left(\dfrac{\pi }{6}+3x\right)+\sin x-\sin\dfrac{\pi }{2}=0$
$\Leftrightarrow 2\sin\left(\dfrac{\pi }{4}-\dfrac{x }{2}\right)\cos\left(\dfrac{\pi }{12}-\dfrac{7x }{2}\right)+2\cos\left(\dfrac{\pi }{4}+\dfrac{x }{2}\right)\sin\left(\dfrac{\pi }{4}-\dfrac{x }{2}\right)=0$
$\Leftrightarrow \left[ {\begin{matrix} \sin\left(\dfrac{\pi }{4}-\dfrac{x }{2}\right)=0\\ \cos\left(\dfrac{\pi }{12}-\dfrac{7x }{2}\right)=-\cos\left(\dfrac{\pi }{4}+\dfrac{x }{2}\right) \end{matrix}} \right.$
$\Leftrightarrow \left[ {\begin{matrix} \sin\left(\dfrac{\pi
}{4}-\dfrac{x }{2}\right)=0\\ \cos\left(\dfrac{\pi }{12}-\dfrac{7x
}{2}\right)=\cos\left(\pi-\dfrac{\pi }{4}-\dfrac{x }{2}\right)
\end{matrix}} \right.$
$\Leftrightarrow \left[ {\begin{matrix} \sin\left(\dfrac{\pi
}{4}-\dfrac{x }{2}\right)=0\\ \cos\left(\dfrac{\pi }{12}-\dfrac{7x
}{2}\right)=\cos\left(\dfrac{3\pi }{4}-\dfrac{x }{2}\right)
\end{matrix}} \right.$
Đến đây đơn giản.Em tự viết nốt nghiệm nhé.
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