$a)_{}$ $x^3+2x^2+3x+2_{}$
$=x^3+x^2+x^2+x+2x+2_{}$
$=x^2.(x+1)+x.(x+1)+2.(x+1)_{}$
$=(x+1)(x^2+x+2)_{}$
$b)_{}$ $x^3+8x^2-8x-1_{}$
$=(x-1)(x^2+x+1)+8x.(x-1)_{}$
$=(x-1)(x^2+x+1+8x)_{}$
$=(x-1)(x^2+9x+1)_{}$
$c)_{}$ $x^3-3x^2-4x+12_{}$
$=x^2.(x-3)-4.(x-3)_{}$
$=(x-3)(x^2-4)_{}$
$=(x-3)(x-2)(x+2)_{}$