00:02
All right, so in this problem, we need to prove two statements using the method of contradiction.
00:09
So part a, so we need to prove that the sum of two prime is a prime.
00:13
If the sum of two primes is a prime, then one of the primes must be two.
00:17
So we suppose that, so by contradiction, we need to suppose that, that a and b are 2 prime, a plus b is a prime, but a and b are not equal to 2.
00:49
All right.
00:51
And then we need to derive a consideration from this.
00:54
So now a and b is a prime different from 2, 2, so we know that a and b have to be out, right? because the only, because the only prime that is even, is 2, and if a and 2 the primes are different from 2, then they have to be odd.
01:32
So we claim that a plus b is even, because the sum of 2 odd number is even, and since a plus b is prime by assumption, we claim the only case that can happen is that a plus b is 2.
01:56
But since a and b is a prime, they have to be at least 2.
02:05
So a and b is a greater 2.
02:07
So a plus b cannot be 2.
02:13
So we have a contradiction...