Question

How do you find all the values that make the expression undefined: `(m - 3)/(3 - m)`?

Answer 1

Your expression is undefined when you get the value `m=3`; in this case you end up with `0/0` which cannot be evaluated.
On the other hand your expression is interesting because collecting `-1` from the numerator you get:
`-(3-m)/(3-m)=-1` !!!