Definition:Ellipse/Directrix

Definition

Let $K$ be the ellipse specified as the locus of points $P$ to a straight line $D$ and a point $F$ such that $PD$ and $PF$ are related by the condition:

$\size {PF} = e \size {PD}$

where $0 < e < 1$.

The line $D$ is known as the directrix of the ellipse.

Also see

• Results about directrices of ellipses can be found here.

Sources

• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): ellipse
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): ellipse