## Precalculus (6th Edition) Blitzer

Given a parabola with vertex at the origin, if the equation is in the form of $x^2=4py$, the curve will open upward if $p\gt0$, downward if $p\lt0$; if the equation is in the form of $y^2=4px$, the curve will open to the right if $p\gt0$, to the left if $p\lt0$.