导数除法法则是 (u/v)'=(u'v-v'u)/(v^2) 你用错了.首先,中间是减号；其次,分母是平方正确形式应当是y‘ = (cosx/x)' = ( - sinx * x - cosx * 1) / x² = - (cosx + xsinx) / x²或者用导数乘法法则 (uv)'=u...