Giải phương trình : Sin^2x + sin^23x= cos^22x + cos^24x Question Giải phương trình : Sin^2x + sin^23x= cos^22x + cos^24x in progress 0 Toán Reagan 1 năm 2021-07-18T14:42:52+00:00 2021-07-18T14:42:52+00:00 1 Answers 81 views 0
Answers ( )
$\Leftrightarrow \dfrac{1-\cos2x+1-\cos6x}{2}=\dfrac{1+\cos4x+1+\cos8x}{2}$
$\Leftrightarrow \cos2x+\cos8x+\cos4x+\cos6x=0$
$\Leftrightarrow 2\cos5x.\cos3x+2\cos5x.\cos x=0$
$\Leftrightarrow 2\cos5x(\cos3x+\cos x)=0$
$\Leftrightarrow 4\cos5x.\cos2x.\cos x=0$
$+) \cos5x=0\Leftrightarrow x=\dfrac{\pi}{10}+\dfrac{k\pi}{5}$
$+) \cos2x=0\Leftrightarrow x=\dfrac{\pi}{4}+\dfrac{k\pi}{2}$
$+) \cos x=0\Leftrightarrow x=\dfrac{\pi}{2}+k\pi$