(X²+1)²-4X²=(X²)²+2X²+1-4X²=(X²)²-2X²+1=(X²-1)²=(X+1)²(X-1)²
(x^2+1)^2-4x^2=(x^2+1-2x)(x^2+1+2x)=(x-1)^2(x+1)^2
