长方形的面积为2a²-8b²（a＞2b＞0）若它的宽为2a-4b
(2a²-8b²)÷(2a-4b)
=2(a²-4b²)÷[2(a-2b)]
=2(a-2b)(a+2b)÷[2(a-2b)]
=a+2b