x^4+x^2+2ax-a^2+1
=x^4+2x^2+1-a^2+2ax-x^2
=(x^2+1)^2-(x-a)^2
=(x^2+x-a+1)(x^2-x+a+1)
方法：把x^2拆成2x^2-x^2,再配方.