f(x)=(2x+1)/(x^2+2)f'(x)=[(2x+1)'(x^2+2)-(2x+1)(x^2+2)']/(x^2+2)^2 根据(u/v)'=(u'v-uv')/v^2=[2(x^2+2)-(2x+1)*2x]/(x^2+2)^2=(2x^2+4-4x^2-2x)/(x^2+2)^2=-2(x^2+x+2)/(x^2+2)^2