Question 261055
Find all numbers for which the rational expression is undefined.
{{{9/(x-5)}}}
:
An expression is undefined when the denominator = 0, therefore
Find x
x - 5 = 0
add 5 to both sides
x = +5
:
You can see when you substitute 5 for x in the original expression
{{{9/(5-5)}}} = {{{9/0}}}, undefined 
:
We don't care about the 9

Response to your comment.  No, the answer is x = 5, that in turn makes the denominator 0 (5 - 5), did the get this?