Does anyone know what 2 prime numbers subtracted together that equals 7?
like this: 7= prime - prime
Anyone plz help me!!!!
It's not possible, and here is a simple proof to show why:
All prime numbers except 2 are odd.
Case 1: One of the prime numbers is 2:
If one of the prime numbers is 2, the other must be 9, which is not a prime number.
Case 2: Neither of the prime numbers is 2:
Then both prime numbers are odd. Let x and y be odd numbers. Then x = 2k + 1 for any integer k (ignoring the restriction for primeness) and y = 2l + 1 for any integer l.
Then x - y = 2k + 1 - (2l + 1) = 2k - 2l = 2(k - 1). Since k - l is an integer, 2(k - l) is an even integer, and thus not 7.
Therefore the are no two prime numbers such that p1 - p2 = 7. QED.
Last edited by Ricky (2005-12-13 09:26:57)
What about 2 and -5? Negatives are probably disallowed, huh?
igloo myrtilles fourmis
Yes i cant use negative numbers and -5-2 is -7 but if your trying to say -2+5 it would only equal3.
Ricky was correct in that there are no solutions to your problem.
Negative numbers are not primes, although one could certainly argue that they should be. But I'm not about to go and change the basic framework of math.