In: Advanced Math
1. When proving If p then q.”
DIRECT PROOF you need to:
CONTRAPOSITION you need to:
CONTRADICTION you need to:
2. Prove by direct proof that if m and n are integers, with m odd and n is even, then 5n + m2 is odd.
3. Prove by contraposition that if x 6= 5 and is irrational, then 4x x − 5 is irrational.
4. Prove the following existential statements by providing a value for x. In both cases, the universe is the set of all real numbers.
a) ∃x x 2 + 5x − 7 = 0
b) ∃x x < 10 → (x − 2) 2 < 0
5. Prove that for any integer n, there exists an even integer k so that n < k + 1 < n + 3.
6. Prove or disprove: If x is rational and y is irrational, then xy is irrational.
7. Prove that there is no positive integer n so that 49 < n 2 < 64.
8. Prove or disprove: ∀x∃y ((x − 3)y = 4x), where the universe of discourse is R for both variables.
9. Prove, by contraposition, that if the product of two real numbers is irrational, then at least one of the two numbers is irrational. (In other words: If x · y is irrational, then x is irrational OR y is irrational.”)
10. Prove, by contradiction, that √ 3 is irrational. You may use the Little Theorem: If m2 is a multiple of 3, then m itself is a multiple of 3