Editing Ellipse (section)

== Orthogonal tangents ==
[[File:Orthoptic-ellipse-s.svg|thumb|Ellipse with its orthoptic]]
{{main|Orthoptic (geometry)}}
For the ellipse <math>\tfrac{x^2}{a^2} + \tfrac{y^2}{b^2} = 1</math> the intersection points of ''orthogonal'' tangents lie on the circle <math>x^2 + y^2 = a^2 + b^2</math>.

This circle is called ''orthoptic'' or [[director circle]] of the ellipse (not to be confused with the circular directrix defined above).