2cosxsinx=sin^22x，最后结果为－4／sinx
∫cos2x/sin^2xcos^2x dx= ∫cos2x/(1/2sin2x)^2 dx=∫2/(sin2x)^2 dsin2x再利用换元积分得=lnsin2xlnsin2X
答案为-2/SIN2X
