# Parabolic Mirror, Theory

*Parabola* is a conic defined by its *focal property*: there is a point - focus - and a line - directrix - and parabola is the locus of points equidistant from the focus and the directrix.

It is known that the tangent to parabola at a point bisects the angle between the segments joining the point to the focus and the directrix.

10 May 2015, Created with GeoGebra

This is equivalent to saying that, if a light source is located at the focus, the rays from the source reflected in the inner surface of the parabolic mirror are parallel. What good is this property? Well, this is how modern car lights work. And this is the principle underlying radio telescopy.

### Conic Sections > Parabola

- The Parabola
- Archimedes Triangle and Squaring of Parabola
- Focal Definition of Parabola
- Focal Properties of Parabola
- Geometric Construction of Roots of Quadratic Equation
- Given Parabola, Find Axis
- Graph and Roots of Quadratic Polynomial
- Greg Markowsky's Problem for Parabola
- Parabola As Envelope of Straight Lines
- Generation of parabola via Apollonius' mesh
- Parabolic Mirror, Theory
- Parabolic Mirror, Illustration
- Three Parabola Tangents
- Three Points on a Parabola
- Two Tangents to Parabola
- Parabolic Sieve of Prime Numbers
- Parabolic Reciprocity
- Parabolas Related to the Orthic Triangle

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