tllau38说
(73)lim(x->0) ln[ 1+ f(x)/sinx] /(arctanx)^2 =Alim(x->0) f(x)/x^3 =?solution :x->0ln(1+ Ax^2) = Ax^2 +o(x^2)//lim(x->0) ln[ 1+ f(x)/sinx] /(arctanx)^2 =Alim(x->0) ln[ 1+ f(x)/sinx] /x^2 =A =>f(x)/sinx = Ax^2 +o(x^2)f(x) = Ax^3 +o(x^3)lim(x->0) f(x)/x^3=lim(x->0) Ax^3/x^3=A