Toán Lớp 11: Giải pt
(2cos x+1) (2sinx + cosx ) = sin 2x + sin x
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Toán Lớp 11: Giải pt
(2cos x+1) (2sinx + cosx ) = sin 2x + sin x
Comments ( 2 )
$\text{(2cos x+1) (2sinx + cosx ) = sin 2x + sin x }$
$\text{pt => ( 2 cosx + 1 ) ( 2sin x + cos x ) }$
$\text{= sin x ( 2 cos x + 1 )}$
$\text{=> ( 2 cos x – 1 ) ( sin x + cos x ) }$
$\text{= 0}$
$\text{⇔ \(\left[ \begin{array}{l}cos x = – \frac{1}{2} \\\sqrt{2} sin ( x + \frac{\pi}{4} ) = 0 \end{array} \right.\) }$
$\text{⇔ \(\left[ \begin{array}{l} x = \pm \frac{2\pi}{3} + k2\pi\\x = \frac{-\pi}{4} + k\pi\end{array} \right.\) }$