个人感觉最好的方法：麦克劳林公式arcsinx = x + x^3/6+o(x^3),sinx = x - x^3/6 + o(x^3),arctanx = x - x^3/3 +o(x^3),tanx = x+x^3/3 + o(x^3)lim(arcsinx-sinx)/(arctanx-tanx)=lim(上述式子代入) = -1/2...