楼主应该是打错了把,漏了一个平方.
原式=[4(a-2b)]²-(a+b)²
=(4a-8b)²-(a+b)²
=(4a-8b+a+b)(4a-8b-a-b)
=(5a-7b)(3a-9b)
=3(5a-7b)(a-3b)