Question 1007106
The fraction means  {{{x-5/x^2-x-12}}} and the value for x which must be excluded is 0 only.  


Not what you meant to write for your fraction expression?  Write it correctly.


Were you missing the needed grouping symbols?
(x-5)/(x^2-x-12)
Very different, and will appear rendered as {{{(x-5)/(x^2-x-12)}}}, which has a different set of undefined values for x than the way you wrote your expression.
The expression is undefined if the denominator is 0.


Factorize the denominator and identify the values of x which make this denominator 0.  That is WHAT to do.  
Undefined for x at -3 and +4.