Answer:

And from this condition we have that:

So then the function is not defined for
and we will have and asymptote in the function for this value of x and would be defined in the rest of the values of x
Explanation:
We assume that we have the following expression:

So then we have a rational expression and we want to find for which value of x the function is not defined. And we can focus for this case in the denominator since we can't divide by 0. So then we can create the following rule:

And from this condition we have that:

So then the function is not defined for
and we will have and asymptote in the function for this value of x and would be defined in the rest of the values of x