Focus of a Parabola

Focus of a Parabola

The focus of a parabola is a fixed point on the interior of a parabola used in the formal definition of the curve.

A parabola is defined as follows: For a given point, called the focus, and a given line not through the focus, called the directrix, a parabola is the locus of points such that the distance to the focus equals the distance to the directrix.

Note: For a parabolic mirror, all rays of light emitting from the focus reflect off the parabola and travel parallel to each other (parallel to the axis of symmetry as well).

 

 

Example:

This is a graph of the parabola with all its major features labeled: axis of symmetry, focus, vertex, and directrix.

 

 

See also

Conic sections, foci of an ellipse, foci of a hyperbola, focal radius