1. Use a direct proof to prove the following statement: If n is an even integer, then n2 - 2n +9 is an odd integer. 2. Use an indirect proof to prove the following statement: Let n be an integer. If 2n +n+5 is odd, then n is even. 3. Prove the following statement: Let n be an integer. Then n2 + 6n - 2 is odd if and only if n is odd. 4. Prove the following statement using an indirect proof: Let a, b be positive real numbers. If a + 6