=(9x^2-1)(x^2-9)=(3x+1)(3x-1)(x+1)(x-1)
=(x^3-y^3)-(x^2-y^2)=(x-y)(x^2+xy+y^2)-(x-y)(x+y)=(x-y)(x^2+xy+y^2-x-y)
=(x-3y)^2-3(x-3y)=(x-3y)(x-3y-3)