Lượng giác ~ \frac{sin^{4}2x+cos^{4}2x}{tan(\frac{\pi }{4}-x)tan(\frac{\pi }{4}+x)}=cos^{4}4x

X

xuanquynh97

ĐK: $tan(\dfrac{\pi}{4}-x) \not=0; tan(\dfrac{\pi}{4}+x) \not=0$

PT \Leftrightarrow $\dfrac{3+cos8x}{4}=4cos^44x$

\Leftrightarrow $2cos^24x+2=4cos^44x$

\Leftrightarrow $cos^24x=1$
 
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