3a^2-2a-1
=(3a+1)(a-1)
x^2-3x^3-9+27x
=x^2(1-3x)-9*(1-3x)
=(1-3x)(x^2-9)
=(1-3x)(x-3)(x+3)
x^2-9y^2-x-3y
=(x-3y)(x+3y)-(x+3y)
=(x+3y)[(x-3y)-1]
=(x+3y)(x-3y-1)