The standard form of an Irrational function is given as:
[tex]\begin{gathered} y=\sqrt{a(x-p)}+q \\ \text{where:} \\ y\geqslant q\text{ and x}\geqslant p \end{gathered}[/tex]In the given function:
[tex]\begin{gathered} g(x)=\sqrt{6-x} \\ \text{Domain: }\left\lbrace x\in R\colon x\leqslant6\right\rbrace \\ \text{Range: }\left\lbrace y\in R,\text{ }y\geqslant0\right\rbrace \end{gathered}[/tex]Therefore, the standard form of g(x) is:
[tex]g(x)=\sqrt{-(x-6)}[/tex]