we know that
the equation of the graph is a horizontal parabola
the equation of a horizontal parabola is of the form
[tex]x=-a(y-k)^{2}+h[/tex] -------> negative because open to the left
where
(h,k) is the vertex of the parabola
in this problem we have
[tex](h,k)=(0,0)[/tex]
Substitute in the equation above
[tex]x=-a(y-0)^{2}+0[/tex]
[tex]x=-ay^{2}[/tex]
therefore
the answer is
[tex]x=-5y^{2}[/tex]
