2x^3+3x^2-4x-1
=x^3-1+x^3+3x^2-4x
=(x-1)(x^2+x+1)+x(x^2+3x-4)
=(x-1)(x^2+x+1)+x(x-1)(x+4)
=(x-1)[(x^2+x+1)+x(x+4)]
=(x-1)(x^2+x+1+x^2+4x)
=(x-1)(2x^2+5x+1)