12a^2b^2-6abc-3ac^2-6a^2bc-c+2ab
12a²b²-6abc-3ac²+6a²bc-c+2ab=-6ab(c-2ab)-3ac(c-2ab)-(c-2ab)=(c-2ab)(-6ab-3ac-1)=-(c-2ab)(6ab+3ac+1)