Answer
$y=-\dfrac{9}{2}x$
(see graph below)
Work Step by Step
Since $y$ varies directly as $x,$ then it follows the model $y=kx.$ Solving for $k$ by substituting the given point, $(
2,-9
),$ results to
\begin{array}{l}\require{cancel}
y=kx
\\
-9=k(2)
\\
\dfrac{-9}{2}=k
\\
k=-\dfrac{9}{2}
.\end{array}
Hence, the direct variation equation is $
y=-\dfrac{9}{2}x
.$
Using a table of values, the graph of $
y=-\dfrac{9}{2}x
$ is shown above.