Question

find all numbers that must be excluded from the domain of the rational expression
show work


9/x-6

Answer 1

6 must be excluded because we cannot have 9/0 as it is undefined.

Answer 2

The domain would be all real numbers excluding +6. Since it would give a zero in the denominator.
If you want a set it is:
\[\left\{ x \in \mathbb{R} | x \ne 6 \right\}\]