why there is two focus in ellipse?and what it indicates?

Dear Baba

For an ellipse there are two foci so that the sum of the distances to the foci from any point on the ellipse is a constant.If we have one focus then it will convert into circle. In terms of the diagram shown below, with "x" marking the location of the foci, we have the equation:

a + b = constant

that defines the ellipse in terms of the distances a and b.

All the best.

AKASH GOYAL

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Approved

As an alternate definition of an ellipse, we begin with two fixed points in the plane. Now consider any point whose distances from these two points add up to a fixed constant d. The set of all such points is an ellipse. The two fixed points that were chosen at the start are called the foci of the ellipse; individually, each of these points is called a focus (pronounced in the usual way).

Approved