Relatively prime numbers

1. Jan 24, 2009

bhavinsinh

I stumbled across this question:Suppose that a and b are relatively prime.Prove that ab and a+b are relatively prime.

2. Jan 24, 2009

MathematicalPhysicist

Use the fact that:
(a+b)/(ab)=1/b+1/a.
If I say more than this, then you wouldn't have anything to do for yourself.

3. Jan 24, 2009

Kurret

Or you could assume that d|ab and prove that then d cant divide a+b (d=/=1).