y=(1+x²)arctanxdy/dx= 2xarctanx + (1+x²)×[1/(1+x²)]= 2xarctanx + 1d²y/dx²= 2arctanx + 2x/(1+x²) 链式求导的一般方法：y = uvwpqrdy/dx = (du/dx)vwpqr + u(dv...