Originally Posted by

**jcir2826** Let p and q be distinct primes. Suppose that H is a proper subset of the integers and H is a group under addition that contains 3 elements of the set { p, P+q, pq, p^q, q^p}

Determine the three elements in H.

Is it a. pq,p^q,q^p

or b. p+q,pq,q^p

c. p, pq, p^q.

I know that c is the right answer but I have not clue why. If H is a group then I would imagine that when I add p +pq I should get another element in H but i dont think so. I cant find an identity or inverse. Thanks