Let me be more explicit, using that (m-a,a)=1 whenever (m,a)=1, I concluded
(m-r1)+(m-r2)+...+(m-rx)=r1+...+rx mod m
and also
(m-r1)+(m-r2)+...+(m-rx)= -r1-r2-...-rx mod m.
So -(r1+...+rx)=r1+...+rx mod m
or 2(r1+...+rx)=0 mod m.
I see that (a,m)=1 immediately implies that (m-a,m)=1,and used that to prove that
2(r1 + r2 + ... +rx) = 0 mod m.
Then when m is odd 2 has a multiplicative inverse mod m, and we can just multiply by that to get r1 + r2 + ... +rx = 0 mod m.
But when m is even, I'm not totally sure, what...
Homework Statement
Prove that if {r1,r2,...rx} is a reduced residue system mod m (where x=\phi(m), m>2), then
r1 + r2 + ... + rx= 0 mod m.
Homework Equations
The Attempt at a Solution
I've been able to prove it pretty simply for odd m and for m=2k where k is odd, but for m with higher powers...