4x^(n+2)-9x^n+6x^(n-1)-x^(n-2)
=x^(n-2)*(4x^4-9x^2+6x-1)
=x^(n-2)*[(2x^2)^2-(3x-1)^2]
=x^(n-2)*(2x^2+3x-1)(2x^2-3x+1)
=x^(n-2)*(2x^2+3x-1)(x-1)(2x-1)