tinh tick phan

S

sky_fly_s2

mình làm thử nhé!


$\int\limits_{pi/6}^{pi/12}\frac{coc2xcos4xcos6xcos8x}{sin4xsin8x+cos4xcos8x}dx$
$\Leftrightarrow \int\limits_{pi/6}^{pi/12}\frac{coc2xcos4xcos6xcos8x}{cos4x}dx$
$\Leftrightarrow \int\limits_{pi/6}^{pi/12}{coc2xcos6xcos8x}dx$
$\Leftrightarrow \frac{1}{2}\int\limits_{pi/6}^{pi/12}{cos6x(cos6x+cos10x)}dx$
$\Leftrightarrow \frac{1}{2}\int\limits_{pi/6}^{pi/12}{cos6x^2+cos6xcos10x}dx$
$\Leftrightarrow \frac{1}{2}\int\limits_{pi/6}^{pi/12}{\frac{cos12x+1}{2}}dx$+$\frac{1}{4}\int\limits_{pi/6}^{pi/12}{cos16x+cos4x}dx$
 
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