Ellipse
If F1 (c, 0) and F2(-c, 0) and are two fixed points in the plane and a is a constant, 0< c < a, then the set of all points P in the plane such that PF1 + PF2 = 2a is an ellipse. F1 and F2 are the foci of the ellipse.
Learn more about ellipse below.
Practice: Answer the following exercises about ellipse.