Blue book pg 681 # 7

snipez90
Thu, 22 Nov 2007 13:54:03 +0000

The fastest solution is better than any “proper” solution. If you want to solve every problem under 30 seconds, you’ll have to become expert at exploring all cases.

Algebraically:
You should recognize that the left hand side factors into (a-b)(a+b) and since 7 is prime, the only resulting possibilities indicate that a must be 4