Prove the following using the method suggested:
(a) Prove the following either by direct proof or by
contraposition:
Let a ∈ Z, if a ≡ 3 (mod 5) and b ≡ 2 (mod 5), then ab ≡ 1 (mod
5).
(b) Prove the following by contradiction:
Suppose a, b ∈ Z. If a² + b²
is odd, then (2|a) ⊕ (2|b), where ⊕ is the exclusive
disjuntion,
i.e. p ⊕ q = (p ∨ q) ∧ ¬(p ∧ q).
(d)...