Question

Let p be a prime number such that p>2. Use the proof by contradiction to show that at least one of numbers p−1 and p+1 is divisible by 4.

Answer 1

p can be 11
-11 is a prime number because it can only be divided by 11 or 1
- 11 + 1 is 12
- 12 is divisible be 4

p can also be 13
-13 is a prime number because it can only be divided by 13 or 1
- 13 minus 1 is 12
- 12 is divisible by 4