# Foci Equation

- Author:
- David

## Finding the foci.

Remember, finding the vertices is quite simple.
You simply add and subtract the major value from it's respected coordinate of the center.
Horizontal: and
Vertical: and
To find the foci it's quite similar.
Horizontal: and
Vertical: and
The next question you may have is: how do I find c?
, this means, larger square minus the smaller square.
As an example, take the ellipse: .
Note that the center is (2,-3) and the vertices are (2,2) and (2,-8).
To find the foci, the larger square is 25, and the smaller is 9.
so
So the foci are (2,-3 4) which is (2,1) and (2,-7)