Proof: Suppose n is any integer. Then
4(n2 + n + 1) − 3n2 = 4n2 + 4n + 4 − 3n2
= n2 + 4n + 4 = (n + 2)2
(by algebra). But (n + 2)2 is a perfect square because n + 2
is an integer (being a sum of n and 2). Hence 4(n2 + n +
1) − 3n2 is a perfect square, as was to be shown.