The Australian Journal of Mathematical Analysis and Applications


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ISSN 1449-5910  

 

Paper Information

Paper Title:

Ellipses of Maximal Area and of Minimal Eccentricity Inscribed in a Convex Quadrilateral

Author(s):

Alan Horwitz

Penn State University,
25 Yearsley Mill Rd., Media, Pa 19063
alh4@psu.edu 
Url: www.math.psu.edu/horwitz

Abstract:

Let – be a convex quadrilateral in the plane and let M1 and M2 be the midpoints of the diagonals of –. It is wellĖknown that if E is an ellipse inscribed in –, then the center of E must lie on Z, the open line segment connecting M1 and M2 . We use a theorem of Marden relating the foci of an ellipse tangent to the lines thru the sides of a triangle and the zeros of a partial fraction expansion to prove the converse: If P lies on Z, then there is a unique ellipse with center P inscribed in –. This completely characterizes the locus of centers of ellipses inscribed in –. We also show that there is a unique ellipse of maximal area inscribed in –. Finally, we prove our most signifigant results: There is a unique ellipse of minimal eccentricity inscribed in –.

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