The domain of any function is the set of numbers for which the function is defined. Since this is a rational function, where the numerator and denominator consist of polynomial expressions, the domain is the set of all real numbers excluding any value of the independent variable that would make the denominator equal zero.
Presuming you mean the function to be defined as:
As opposed to ,
Then we simply need to exclude the value
Hence the domain, expressed in set builder notation, is
