发布时间:2019-08-27 13:19:05
(a-b)(a-4b)+ab
=a²-5ab+4b²+ab
=a²-4ab+4b²
=(a-2b)²
=a^2-4ab-ab+4b^2+ab
=a^2-4ab+4b^2
=(a-2b)^2