(a-b)(a+2)-(a+b)(a-2)=а2-аb-2a-2b-(a2+ab-2a-2b)= а2-аb-2a-2b-a2-ab+2a+2b=-2ab (x+y)(x-y)-(x-1)(x-2)=x2-y2-(x2-x-2x+2)=x2-y2-x2+x+2x-2=3x-y2-2