lim(tanx-sinx)/sin^3x=limsinx(1/cosx-1)/sin^3x=lim(1-cosx)/[sin^2x*cosx]=lim2(sinx/2)^2/[4(sinx/2)^2(cosx/2)^2*cosx]=lim1/[2(cosx/2)^2*cosx]当x→2π时cosx/2→ -1cosx→ 1原极限=1/2第3个= 的分母怎么转化的，麻烦了~sinx=2sinx/2cosx/2sin^2x=4(sinx/2)^2(cosx/2)^2怎么啦,二倍角公式有问题吗