简单分析一下，答案如图所示
lim(x->0)(arctanx-x)/[xln(1+2x^2)] =lim(x->0)(arctanx-x)/x^3 =lim(x->0)[1/(1+x^2)-1]/(3x^2) =lim(x->0)-x^2/[(1+x^2)(3x^2)] =lim(x->0)-x^2/[(3x^2)] =-1/3
