[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}\\\\
-------------------------------\\\\
\textit{we also know that }
\begin{cases}
y=-2\\
x=4
\end{cases}\implies -2=k4\implies \cfrac{-2}{4}=k
\\\\\\
-\cfrac{1}{2}=k\qquad therefore\qquad \boxed{y=-\cfrac{1}{2}x}
\\\\\\
\textit{now, if y = 5, what is \underline{x}?}\qquad 5=-\cfrac{1}{2}x[/tex]
