S(x^2 +1)/(x^4 +1)dx =S(1+1/x^2)/(x^2+1/x^2)dx =S1/[(x-1/x)^2+2] d(x-1/册竖x) t=x-1/x =S1/(t^2+2) dt =根2/猜姿橡2*arctan(t/根2）+c =根穗旁2/2*arctan((x-1/x)/根2）+c
