Directrices
of a Hyperbola
Two parallel lines which
are perpendicular to the major
axis of a hyperbola. The directrices are between
the two parts of a hyperbola and
can be used to define it as follows: A hyperbola is the locus of
points such that the ratio of the distance to the nearer focus to the distance
to the nearer directrix equals a constant that
is greater than one. This constant is the eccentricity.
See
also
Directrices of
an ellipse, directrix of a parabola
