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

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