4-（x²-4x+2）²
=(2+x^2-4x+2)(2-x^2+4x-2)
=(x^2-4x+4)(-x^2+4x)
=-x(x-4)(x-2)^2
x^4-2x^2+1
=(x^2-1)^2
=(x+1)^2*(x-1)^2
有问题追问.