1.x^4+x^2+2ax-a^2+1
=x^4+2x^2-x^2+2ax-a^2+1
=(x^4+2x^2+1)-(x^2-2ax+a^2)
=(x^2+1)^2-(x-a)^2
=(x^2+1+x-a)(x^2+1-x+a)
2.X^5+X+1
＝x^5-x^2+x^2+x+1
=x^2(x^3-1)+(x^2+x+1)
=x^2*(x-1)(x^2+x+1)+(x^2+x+1)
=(x^2+x+1)(x^3-x^2+1)
3..x的平方-6y的平方-12z的平方+xy-xz+17yz
=x^2+x(y-z)-(6y^2-17yz+12z^2)
=x^2+x(y-z)-(2y-3z)(3y-4z)
=(x-2y+3z)(x+3y-4z)