lim(x→0){[∫（上x下0）ln(cost)dt]/x^3}

用洛笔答法则,=lim ln(cosx) / (3x²)=lim ln(1+ cosx -1) / (3x²)=lim (cosx -1) / (3x²) 【等价无穷小代换】= -lim (1-cosx) / (3x²)= -lim (x²/2) / (3x²) 【等价无穷小代换】= -1/...