Question 313023
A rational expression is undefined if the denominator is zero.  In this case, the denominator is 
x^2 -9


Set this denominator equal to zero, factor the left side, and solve for x:
(x-3)(x+3)=0
x-3=0 or x+3=0
x=3 or x=-3


Dr. Robert J. Rapalje, Retired