y=f[(x-1)/(x+1)],f'(x)=arctanx^2,求dy/dx,dy两边对x求导：dy/dx=f'[(x-1)/(x+1)]*2/（x+1)^2=arctan[(x-1)/(x+1)]^2*2/（x+1)^2dy=f'[(x-1)/(x+1)]*2/（x+1)^2=arctan[(x-1)/(x+1)]^2*2/（x+1)^2*dx