Answer
$x^2=-2y$
Work Step by Step
It is a parabola with vertical axis. Directrix: $y=-p$
Directrix: $y=-p=\frac{1}{2}$
$p=-\frac{1}{2}$
Equation: $x^2=4py$
$x^2=4(-\frac{1}{2})y$
$x^2=-2y$
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