lim 1/x*(1/sin x-1/x)变化得：=lim (x-sin x)/(sin x*x^2) （sin x 与 x 是等价无穷小）=lim (x-sin x)/(x^3) （属于0/0型,可用洛必塔）=lim (1-cos x)/(3x^2) =lim 2(sin x/2)^2/(3x^2) （sin x/2 与 x/2 是等价无...