Definition:Directrix

Disambiguation

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Directrix may refer to:

Directrix of Ruled Surface

A directrix is a curve which defines the generators of a ruled surface.

Directrix of Conic Section

Let $K$ be a conic section specified in terms of:

a given straight line $D$

a given point $F$

a given constant $e$

where $K$ is the locus of points $P$ such that the distance $p$ from $P$ to $D$ and the distance $q$ from $P$ to $F$ are related by the condition:

$q = e p$

The line $D$ is known as the directrix of the conic section.

Directrix of Conchoid

Let $\KK$ be a conchoid.

Let $\CC$ be the curve with respect to which the conchoid is constructed.

$\CC$ is known as the directrix of $\KK$.

Also see

• Results about directrices can be found here.

Linguistic Note

The plural of directrix is directrices.