7 A student wishes to prove that, for all positive integers \(a\) and \(b , a ^ { 2 } - 4 b \neq 2\).
- Prove that \(a ^ { 2 } - 4 b = 2 \Rightarrow a\) is even.
- Hence or otherwise prove that, for all positive integers \(a\) and \(b , a ^ { 2 } - 4 b \neq 2\).