极限lim(x趋向0)(∫ln(1+t)dt)/x^4 上限x^2下限0
=lim(x->0) ln(1+x²) ·2x/4x³
=1/2lim(x->0) ln(1+x²)/x²
=1/2lim(x->0) (x²)/x²
=1/2