The Homothety with center P and ratio k,
denoted by h(P,k), is the transformation such that
the image of a point M is the point N such that
P, M and N are collinear, if k > 0, M and N lie on the same side
of P, if k < 0, P is between M and N, and
Triangles
ABC
and
A1B1C1
are homothetic triangles if there exists homothety
such that the second triangle is the homothetic image of the first
(if this is the case, the first triangle
is homothetic image of the second one, too).
In general, two figures are homothetic,
if the second figure is the
homothetic image of the second one.
Then the homothetic center of the homothety is said to be
the homothetic center of the figures.