3x3 + 6x2 + 3x - 12xy2
= 3x(x2 + 2x + 1 - 4y2)
= 3x[(x + 1)2 - (2y)2]
= 3x(x + 1 + 2y)(x - 2y + 1)
\(3x^3+6x^2+3x-12xy^2\)
\(=3x\left(x^2+2x+1-4y^2\right)\)
\(=3x\left[\left(x+1\right)^2-\left(2y\right)^2\right]\)
\(=3x\left(x+1-2y\right)\left(x+1+2y\right)\)