Focal Definition of Ellipse

The applet below illustrates the focal property of the ellipse: given two points F and F' (called the foci of the ellipse), ellipse is the locus of points P the sum of whose distances to the foci is constant: PF + PF' = const. This property is often taken for a definition of ellipse. (A different demonstration can be found elsewhere.)

This applet requires Sun's Java VM 2 which your browser may perceive as a popup. Which it is not. If you want to see the applet work, visit Sun's website at https://www.java.com/en/download/index.jsp, download and install Java VM and enjoy the applet.

What if applet does not run?

Conic Sections > Ellipse

• What Is Ellipse?
  
• Analog device simulation for drawing ellipses
• Angle Bisectors in Ellipse
• Angle Bisectors in Ellipse II
• Between Major and Minor Circles
• Brianchon in Ellipse
• Butterflies in Ellipse
• Concyclic Points of Two Ellipses with Orthogonal Axes
• Conic in Hexagon
• Conjugate Diameters in Ellipse
• Dynamic construction of ellipse and other curves
• Ellipse Between Two Circles
• Ellipse in Arbelos
• Ellipse Touching Sides of Triangle at Midpoints
• Euclidean Construction of Center of Ellipse
• Euclidean Construction of Tangent to Ellipse
• Focal Definition of Ellipse
• Focus and Directrix of Ellipse
• From Foci to a Tangent in Ellipse
• Gergonne in Ellipse
• Pascal in Ellipse
• La Hire's Theorem in Ellipse
• Maximum Perimeter Property of the Incircle
• Optical Property of Ellipse
• Parallel Chords in Ellipse
• Poncelet Porism in Ellipses
• Reflections in Ellipse
• Three Squares and Two Ellipses
• Three Tangents, Three Chords in Ellipse
• Van Schooten's Locus Problem
• Two Circles, Ellipse, and Parallel Lines

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