Answer
The equation $y=-{{x}^{2}}$.
Work Step by Step
The equation is equivalent to $y=-{{\left( x-0 \right)}^{2}}+0$.
Now choose some value of x on both sides of the vertex and compute the corresponding y value.
$\begin{matrix}
x & y \\
0 & 0 \\
1 & -1 \\
2 & -4 \\
-1 &-1 \\
-2 & -4 \\
\end{matrix}$
Now plot all the values of x and y on the rectangular coordinate system and join each point with one another to form a parabola.
It can be concluded that the graph opens down because the coefficient of ${{x}^{2}}$ is negative
