Conic Sections: Parabola
A parabola is defined as locus of points in a plane which are equidistant from a given point (focus) and a given line (directrix).
A parabola with vertex (h, k) and axis parallel to a coordinate axis may be expressed by:
(x − h)2 = 4p(y − k) for vertical axis of symmetry
or
(y − k)2 = 4p(x − h) for horizontal axis of symmetry
or
(y − k)2 = 4p(x − h) for horizontal axis of symmetry
The parabola opens in the positive direction if p > 0 and negative direction for p < 0. For each case, |c| equals the distance between the vertex and focus (or directrix).