3x^2-2x-4
=3(x^2-2x/3+1/9)-4-1/3
=3(x-1/3)^2-13/3
=3[(x-1/3)^2-13/9]
=3(x-1/3+√13/3)(x-1/3-√13/3)
=(1/3)(3x+√13-1)(3x-√13-1)