Answer
$x^{2}=-40y$
Work Step by Step
The equation will have an $x^{2}$ term as the axis of symmetry is y-axis.
As the parabola opens downwards, the coefficient of y is negative.
Therefore, the equation of the parabola is
$x^{2}= -4ay$
Given: $a=10$
$\implies$ $x^{2}=-40y$
