[tex] \bf \qquad \qquad \textit{direct proportional variation}
\\\\
\textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby
\begin{array}{llll}
k=constant\ of\\
\qquad variation
\end{array}\\\\
------------------------------- [/tex]
[tex] \bf \textit{we also know that }
\begin{cases}
y=-8\\
x=20
\end{cases}\implies -8=k20\implies \cfrac{-8}{20}=k
\\\\\\
-\cfrac{2}{5}=k\qquad therefore\qquad \boxed{y=-\cfrac{2}{5}x}
\\\\\\
\textit{when x = -4, what is \underline{y}?}\qquad y=-\cfrac{2}{5}(-4)\implies y=\cfrac{8}{5} [/tex]
