复合函数分别求导再相乘.
即 (dy/du)*(du/dx)=(3u^2)*2x ,再把u=x^2代回去,就得3(x^2+1)^2*2x能分别把dy/dx,dx/du能具体写出来吗==谢谢了你设u=x^2+1，则y=u^3

y'=(dy/du)*(du/dx)
=(u^3)' *(x^2+1)'
=(3u^2) * 2x
然后将u=x^2+1代入，得
y'=3*(x^2+1)^2*2x