How to prove that the foot of perpendicular drawn from a focus to any tangent of an ellipse lies on its auxiliary circle?

2.9k Views Asked by At

One way is to find the foot of perpendicular and directly putting it into the equation of auxiliary circle. But that is quite a lengthy proof, is there any other short method to prove this property?

1

There are 1 best solutions below

0
On

OUTLINE

Let the foci be $F,F'$. Let $P$ be a point on the ellipse and let the feet for the perpendiculars from $F,F'$ to the tangent at $P$ be $T,T'$. Let the lines $F'P,FT$ meet at $X$. Let $O$ be the centre of the ellipse.

Show that $FPT,XPT$ are congruent. Using the focal distances property show that $F'X=2a$. Prove that $OT$ is parallel to $F'X$. Prove that $OT=a$.