#x^3 -3x^2 -4x +12" "larr# group into pairs
#=(x^3 -3x^2)+ (-4x +12)" "larr# there must be a #+# between.
#x=^2(x-3)color(blue)(-4(x-3))" "larr div color(blue)(-4)# out as the factor to change the signs.
#=(x-3)(x^2-4)" "larr# factors further as difference of squares.
#=(x-3)(x+2)(x-2)#