也是( 根据公式(u/v)'=(u'v-uv')/v^2)
y=(3-x^2)/(3+x^2)
y'=[(3-x^2)'(3+x^2)-(3-x^2)(3+x^2)']/(3+x^2)^2
=[-2x(3+x^2)-2x(3-x^2)]/(3+x^2)^2
=(-6x-2x^3-6x+2x^3)/(3+x^2)^2
=-12x/(3+x^2)^2