Giải phương trình : Sin^2x + sin^23x= cos^22x + cos^24x

0 bình luận về “Giải phương trình : Sin^2x + sin^23x= cos^22x + cos^24x”

1. $\Leftrightarrow \dfrac{1-\cos2x+1-\cos6x}{2}=\dfrac{1+\cos4x+1+\cos8x}{2}$

   $\Leftrightarrow \cos2x+\cos8x+\cos4x+\cos6x=0$

   $\Leftrightarrow 2\cos5x.\cos3x+2\cos5x.\cos x=0$

   $\Leftrightarrow 2\cos5x(\cos3x+\cos x)=0$

   $\Leftrightarrow 4\cos5x.\cos2x.\cos x=0$

   $+) \cos5x=0\Leftrightarrow x=\dfrac{\pi}{10}+\dfrac{k\pi}{5}$

   $+) \cos2x=0\Leftrightarrow x=\dfrac{\pi}{4}+\dfrac{k\pi}{2}$

   $+) \cos x=0\Leftrightarrow x=\dfrac{\pi}{2}+k\pi$

   Bình luận