Find a multiplicative inverse of $a=11$ modulo $m=13$.
What is this saying?
This seems like such a simple question, I just don't understand what it is asking for.
An additional question related to this I have is:
If $a$ has a multiplicative inverse modulo $m$, explain why $\gcd(a,m)=1$.
Is this also saying $ab \equiv 1 (mod \space m)$? Do $a$ and $m$ have to be prime since the $\gcd(a,m)=1$?
Thanks again.