(5a+6)²-1=(5a+6-1)(5a+6+1)=(5a+5)(5a+7)=5(a+1)(5a+7) 25-(a+7)²=(5-a-7)(5+a+7)=(-2-a)(12+a)=-(a+2)(a+12) 9m²-(1+2m)²=(3m-1-2m)(3m+1+2m)=(m-1)(5m+1)