Category:Definitions/Harmonic Ratios

This category contains definitions related to Harmonic Ratios.
Related results can be found in Category:Harmonic Ratios.

Let $A$, $B$, $C$ and $D$ be points on a straight line.

Let the cross-ratio $\set {A, B; C, D}$ of $A$, $B$, $C$ and $D$ be equal to $-1$:

$\dfrac {AC / CB} {AD / DB} = -1$

that is:

$\dfrac {AC \cdot DB} {AD \cdot CB} = -1$

Then $\set {A, B; C, D}$ is known as a harmonic ratio.