1) ........=a^4+2a²b²+b^4 - a^4 - a²b²=a²b²+b^4=b²(a²+b²)
2) ...=m²+mn-m²-2mn-n²= - mn - n²= - n(nm+n)
3) ....=(12x²+6x)(5y+7z+7z-5y)=6x*14z*(2x+1)=84xz(2x+1)
4) .....=(5y-7z)(12x²-6x+12x²+6x)=(5y-7z)*24x²
5) .....=5x(3a² -2b)+(3a² -2b)+(3a²-2b)3y=(3a² - 2b)(5x+1+3y)
6) .....=5a(4a-7b)-8b(4a-7b)-(4a-7b)=(4a-7b)(5a-8b-1)
7) ......=(x²-x-1)(y+2)-(x²-x-1)(z-12)=(x²-x-1)(y+2-z-12)=(x²-x-1)(y-z-10)
8) ....=(2k²-3m)(y²-y+2)+(2k²-3m)(y²-y+2)=2(2k²-3m)(y²-y+2)