Question

5.34. Prove that if n is an odd integer, then 7n − 5 is even by

(a) a direct proof, (b) a proof by contrapositive and (c) a proof by contradiction.​

Answer 1

Any) odd integer can be written as 2k+1 (k is integer)
7(2k+1)-5 = 14k - 2 = 2(7k-1)
Thus it is even