$a)_{}$ $2x^2+3x-2_{}$
$=2x^2+4x-x-2_{}$
$=2x.(x+2)-(x+2)_{}$
$=(x+2)(2x-1)_{}$
$b)_{}$ $3x^2-6xy+3y^2-12z^2_{}$
$=3.(x^2-2xy+y^2-4z^2)_{}$
$=3.[ (x-y)^2-4z^2]_{}$
$=3.(x-y-2z)(x-y+2z)_{}$
$c)_{}$ $x^3-3x^2-9x+27_{}$
$=x^2.(x-3)-9.(x-3)_{}$
$=(x-3)(x^2-9)_{}$
$=(x-3)(x+3)(x-3)_{}$
$=(x-3)^2.(x+3)_{}$