有没有好办法？

来源: 于 2012-03-10 19:31:33 [旧帖] [给我悄悄话] 本文已被阅读：次

 

Let A be the set of all integers of the form a^2+4*a*b+b^2 where a and b are integers,

How can I prove that if x, y belong to A, x*y also belongs to A?

 

Thanks in advance