[tex]\qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad \stackrel{\textit{constant of variation}}{y=\stackrel{\downarrow }{k}x~\hfill } \\\\ \textit{\underline{x} varies directly with }\underline{z^5}\qquad \qquad \stackrel{\textit{constant of variation}}{x=\stackrel{\downarrow }{k}z^5~\hfill } \\\\[-0.35em] ~\dotfill[/tex]
[tex]\stackrel{\textit{"y" varies directly with "x"}}{y=kx}~\hfill \textit{we also know that} \begin{cases} x= 35\\ y = 7 \end{cases} \\\\\\ 7=k(35)\implies \cfrac{7}{35}=k\implies \cfrac{1}{5}=k~\hfill \boxed{y=\cfrac{1}{5}x}[/tex]
