Question 556480
Assume the opposite of what you are trying to prove is true, find a contradiction. 


For example, if you wanted to prove that there are infinitely many prime numbers, first assume that there are a finite number of primes. If you let N = 2*3*5*7*...*p where p is the "largest" prime, then N+1 must either be prime or be the product of two primes. However, N+1 cannot be divisible by any prime less than or equal to p, so if N+1 is composite, a larger prime divides it --> contradiction.