x^2+x-2
=(x+2)(x-1)
x^2+2x-3
=(x+3)(x-1)
x^2+2x+1
=(x+1)^2
x^2-4x+4
=(x-2)^2
x^2-3x+2
=(x-2)(x-1)
x^3-2x^2+x
=x(x^2-2+1)
=x(x-1)^2
x^4-x^2
=x^2(x^2-1)
=x^2(x-1)(x+1)