分解因式：x+4x-1
解 (x^2+1)^2-4x^2=(x^2+1+2x)(x^2+1-2x)=(x+1)^2(x-1)^2
(x^2+1)^2-4x^2=（x^2-2x+1）（x^2+2x+1）=（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
