[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}\qquad \textit{we also know that} \begin{cases} x=-4\\ y=6 \end{cases} \\\\\\ 6=k(-4)\implies \cfrac{6}{-4}=k\implies -\cfrac{3}{2}=k~\hfill \boxed{y=-\cfrac{3}{2}x}[/tex]
