Correct. When $\displaystyle{x}={0}\usepackage{cmbright}\Huge\$ , the expression becomes $\displaystyle\frac{{{x}+{1}}}{{9}}\div\frac{{x}}{{3}}=\frac{{1}}{{9}}\div\frac{{0}}{{3}}=\frac{{1}}{{9}}\div{0}\usepackage{cmbright}\Huge\$ . Since division by 0 is undefined, this value must be excluded from the domain of the expression.