Question 359031
Find all numbers for which the rational expression is undefined. 

m^3-7m / m^2-81
----
The denominator cannot be zero.
---
Solve m^2-81 = 0
(m-9)(m+9) = 0
m = 9 or m = -9
----------------------
The expression is undefined for m = 9 and for m = -9.
------------
Cheers,
Stan H.