

mình làm thử nhé!
pi/6∫pi/12sin4xsin8x+cos4xcos8xcoc2xcos4xcos6xcos8xdx
⇔pi/6∫pi/12cos4xcoc2xcos4xcos6xcos8xdx
⇔pi/6∫pi/12coc2xcos6xcos8xdx
⇔21pi/6∫pi/12cos6x(cos6x+cos10x)dx
⇔21pi/6∫pi/12cos6x2+cos6xcos10xdx
⇔21pi/6∫pi/122cos12x+1dx+41pi/6∫pi/12cos16x+cos4xdx