Beginning & Intermediate Algebra
A circle is an ellipse in which the two foci coincide at the same point.
A circle is an ellipse where the distance between the foci is greater than the major axis.
A circle is an ellipse with two distinct foci in which the sum of the distances from any point on the circle to the two foci is variable.
A circle is an ellipse in which the distances from any point on the circle to two distinct foci are always equal.