I am having some trouble with this problem:

(x-1)/(x+3)

After I have evaluated the problem, no critical numbers exist. But according to the multiple choice answer it states there a critical number.

This is my understanding of critical numbers:

if f'(c)= 0 or f'(c)= undefined and c lies in the domain of the function of f(x)

a critical number exist.

According to everything I done, f'(x) = -3 this number is undefined and also undefined at f(x) so the number is not a critical number.

Could someone verify this for me before I present this to the teacher?

Thanks!