Derive the equation of a parabola from a focus and directrix.
Determine the opening direction of a parabola from its focus and directrix
Problem
A parabola has focus \((0,~2)\) and directrix \(y~=~-2\). Locate the vertex midway between them, compare the focus position with the vertex, and state the opening direction with justification.
Big Picture
What this problem is really about
Opening direction depends on where the focus lies relative to the vertex, not on the directrix orientation alone. We’ll use the line’s perpendicular direction for the axis, locate the midpoint vertex, compare the focus position with it, apply the toward-focus rule, and confirm with signed p and standard form.
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