limx→0{(tanx-x)/x^3}
问题描述：
limx→0{(tanx-x)/x^3}
答
lim(x→0){(tanx-x)/x^3}
=lim(x→0{(tanx-x)'/(x^3)'
=lim(x→0{(1/cosx^2-1)'/(3x^2)'
=lim(x→0) (2sinx/cosx^3)/6x]
=(1/3)lim(x→0[(sinx/x)(1/cosx^3)
=1/3