Correct. $\displaystyle\frac{{{{t}}^{{2}}{s}}}{{{r}{s}}}+\frac{{{r}{{s}}^{{2}}}}{{{r}{t}}}=\frac{{{{t}}^{{3}}+{r}{{s}}^{{2}}}}{{{r}{t}}}\usepackage{cmbright}\Huge\$ ; the domain excludes $\displaystyle{s}={0},{r}={0}\usepackage{cmbright}\Huge\$ and $\displaystyle{t}={0}\usepackage{cmbright}\Huge\$ because these values yield a denominator of 0.