Answer:
[tex]x \ne 1[/tex]
Step-by-step explanation:
I am assuming you mean [tex]y=\frac{3}{x-1}[/tex] which would by typed on one line as
y = 3/(x - 1).
The function's formula has a denominator, so one must avoid having the denominator equal to 0 (division by 0 is undefined).
If x - 1 = 0, then x = 1. The number to avoid is 1.
The domain is all real numbers except 1.