Question

Which two fixed points define the shape of an ellipse?

A. Center and focus
B. Focus and directrix
C. Two foci
D. Vertex and focus

Answer 1

For every ellipse E there are two distinguished points, called the foci, and a fixed positive constant d greater than the distance between the foci, so that from any point of the ellipse, the sum of the distances to the two foci equals d .