Given:
[tex]R(x)=\frac{4x}{x-3}[/tex]Domain : Domain of function is define as a all possible input value for the function not consider which types of input that contain infinity of undefine from of function.
So:
[tex]\frac{4x}{x-3}[/tex]Here
[tex]\begin{gathered} x-3\ne0 \\ x\ne3 \end{gathered}[/tex]Domain is:
[tex]\mleft\lbrace x\in R\colon x\ne3\mright\rbrace[/tex]Function acepect all real value but at x=3 the function is undefine form.