\(2x^4+12x^3+14x^2-2x-6\\ =2x^4+2x^3+10x^3+10x^2+4x^2+4x-6x-6\\ =2x^3\left(x+1\right)+10x^2\left(x+1\right)+4x\left(x+1\right)-6\left(x+1\right)\\ =\left(2x^3+10x^2+4x-6\right)\left(x+1\right)\)
2x4 + 12x3 + 14x2 - 2x - 6
= 2x4 + 2x3 + 10x3 + 10x2 + 4x2 + 4x - 6x - 6
= ( x + 1 ) ( 2x3 + 10x2 + 4x - 6 )