2sin3x -2sinxcosx-sin5x=0 giup mk voi cam on bang ca tam long
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Giải thích các bước giải:
$2\sin 3x-2\sin x\cos x-\sin 5x=0$
$\rightarrow 2\sin 3x=\sin 2x+\sin 5x$
$\rightarrow 2\sin 3x=2\sin \dfrac{7x}{2}\cos \dfrac{3x}{2}$
$\rightarrow \sin 3x=\sin \dfrac{7x}{2}\cos \dfrac{3x}{2}$
$\rightarrow 2\sin \dfrac{3x}{2}\cos \dfrac{3x}{2}=\sin \dfrac{7x}{2}\cos \dfrac{3x}{2}$
$\rightarrow\cos \dfrac{3x}{2}( 2\sin \dfrac{3x}{2}-\sin \dfrac{7x}{2})=0$
$+)\cos \dfrac{3x}{2}=0\rightarrow x=\dfrac{\pi}{3}+\dfrac{4k\pi}{3}, x=\pi+\dfrac{4k\pi}{3}$
$+) 2\sin \dfrac{3x}{2}-\sin \dfrac{7x}{2}=0$