Definition:Focus

Disambiguation

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Focus may refer to:

• Geometry:
  • Focus of Conic Section
    • Focus of Ellipse
    • Focus of Parabola
    • Focus of Hyperbola

Also see

• Results about foci can be found here.

Linguistic Note

The word focus is of Latin origin, hence its irregular plural form foci.

It was introduced into geometry by Johannes Kepler when he established his First Law of Planetary Motion.

The word in Latin means fireplace or hearth, which is appropriate, considering the position of the sun.

The pronunciation of foci has a hard c, and is rendered approximately as foke-eye.

Beware the solecism of pronouncing it fo-sigh, which is incorrect.