(1+x^2)^2-4x^2 =(1+x^2-2x)(1+x^2+2x)=[(x+1)(x-1)]^2
=1+2X*2+X*4-4X*2=1-2X*2+X*4=(1-X*2)*2
(1+x^2)^2-4x^2 = (1+x^2)^2-(2x)^2 = (1+x^2-2x)(1+x^2+2x) = (1-x)^2*(1+x) ^2
x^4+1-2X^2=(x^2-1) ^2