# Foci of an Ellipse

Written by Jerry Ratzlaff on . Posted in Plane Geometry

## Foci of an Ellipse

Foci is a point used to define the conic section.  $$F$$ and $$G$$ seperately are called "focus", both togeather are called "foci".

### Foci of an Ellipse formula

$$c^2 = a^2 - b^2$$          $$center \; to \; focus^2 \;=\; semi-major \; axis^2 \;-\; semi-minor \; axis^2$$

Where:

$$c$$ = length center to focus

$$a$$ = length semi-major axis

$$b$$ = length semi-minor axis

$$F$$ and $$G$$ = focus