[tex]\qquad \qquad \textit{inverse proportional variation} \\\\ \textit{\underline{y} varies inversely with \underline{x}} ~\hspace{6em} \stackrel{\textit{constant of variation}}{y=\cfrac{\stackrel{\downarrow }{k}}{x}~\hfill } \\\\ \textit{\underline{x} varies inversely with }\underline{z^5} ~\hspace{5.5em} \stackrel{\textit{constant of variation}}{x=\cfrac{\stackrel{\downarrow }{k}}{z^5}~\hfill } \\\\[-0.35em] \rule{34em}{0.25pt}[/tex]
[tex]\stackrel{\textit{"z" inversely proportional to "t"}}{z=\cfrac{k}{t}}\qquad \textit{we also know that} \begin{cases} t=9\\ z=28 \end{cases} \\\\\\ 28=\cfrac{k}{9}\implies 252=k~\hfill \boxed{z=\cfrac{252}{t}} \\\\\\ \textit{when t = 12, what is "z"?}\qquad z=\cfrac{252}{12}\implies z=21 \\\\\\ \textit{when z = 36, what is "t"?}\qquad 36=\cfrac{252}{t}\implies t=\cfrac{252}{36}\implies t=7[/tex]
