原式=lim(x->0) ln[(sinx/x)^(1/x^2)]=lim(x->0) ln{{(1+sinx/x-1)^[1/(sinx/x-1)]}^[(sinx/x-1)/x^2]}=lim(x->0) ln{e^[(sinx/x-1)/x^2]}=lim(x->0) (sinx-x)/x^3=lim(x->0) (cosx-1)/3x^2=lim(x->0) (-x^2/2)/3x^2=-1/6
