Explanation:
In this exercise we have the following function:
[tex]f(x)=\frac{9}{x-5}[/tex]
So the domain of this function is the set of all real numbers such that [tex]x=\neq 5[/tex]
Why?
Remember that the domain of a function are those x-values for which the function is defined. In this case, for [tex]x=5[/tex] the function is undefined, therefore x can't be 5.
