\(2x^3+x^2-4x-12\)
\(=2x^3+5x^2+6x-4x^2-10x-12\)
\(=\left(2x^3-4x^2\right)+\left(5x^2-10x\right)+\left(6x-12\right)\)
\(=2x^2\left(x-2\right)+5x\left(x-2\right)+6\left(x-2\right)\)
\(=\left(x-2\right)\left(2x^2+5x+6\right)\)
\(=x^2-4x-4\)
\(=\left(x-2-2\sqrt{2}\right)\left(x-2+2\sqrt{2}\right)\)