Question

What is a focus in an ellipse?

Answer 1

The focus of an ellipse:

1. Ellipse is a collection of points such that the sum of the distance of the points from two fixed points is constant. These two fixed points are known as foci.
2. An ellipse has two foci.
3. The foci of an ellipse lie either on the major axis.
4. The coordinate of foci of an ellipse whose center is origin and major axis is $x-$axis is $\left(\pm ae,0\right)$, where $e=\sqrt{1-\frac{b^2}{a^2}}$, $a$ is the length of the semi-major axis and $b$ is the length of the semi-minor axis.