Definition:Harmonic Conjugates

Definition

Harmonic Range

Let $AB$ and $PQ$ be line segments on a straight line such that $\tuple {AB, PQ}$ is a harmonic range.

Then $P$ and $Q$ are said to be harmonic conjugates with respect to $A$ and $B$.

Harmonic Pencil

Let $AB$ and $PQ$ be line segments on a straight line such that $\tuple {AB, PQ}$ is a harmonic range.

Let $O$ be a point which is not on the straight line $AB$.

Let $\map O {AB, PQ}$ be the harmonic pencil formed from $O$ and $\tuple {AB, PQ}$.

The rays $OP$ and $OQ$ are said to be harmonic conjugates with respect to $OA$ and $OB$.