folosesti formula a²-b²=(a+b)(a-b), unde a=12a-1 iar b=1
(12a-1)²-1=(12a-1+1)(12a-1-1)=12a(12a-2)=24a(6a-1)
121-(11-9x)²= (11+11-9x)(11-11+9x)=9x(22-9x), am considerat in formula a=11, b=11-9z
(2a+6b)²-24ab=4a²+24ab+36b²-24ab=4a²+36b²=4(a²+9b²), am folosit formula (a+b)²=a²+2ab+b², unde am inlocuit a=2a si b=6b
a²b²-(ab-7)²=(ab+ab-7)(ab-ab+7)=7(2ab-7)