Discrete mathematics

10 . Definition We say 3 divides b, notated 318 when b = 3 for some integer & bis a multiple 11. Definition An integer is sane if 3 (n' + n). (a) Give a counterexample to the following: All odd integers are sane. (b) Give a direct proof of the following: If 3, then n is sane. (c) Prove by contradiction: If n = 3j + 2 for some integer j, then n is sane