Steiner line
Steiner line
Let be a triangle with orthocenter
is a point on the circumcircle
of
Let and
be the reflections of
in three lines which contains edges
and
respectively.
Prove that and
are collinear. Respective line is known as the Steiner line of point
with respect to
Proof
Let and
be the foots of the perpendiculars dropped from
to lines
and
respectively.
WLOG, Steiner line cross at
and
at
The line is Simson line of point
with respect of
is midpoint of segment
homothety centered at
with ratio
sends point
to a point
Similarly, this homothety sends point to a point
, point
to a point
therefore this homothety send Simson line to line
Let
is simmetric to
Quadrungle is cyclic
at point
Similarly, line
at
According the Collins Claim is
therefore
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Collings Clime
Let triangle be the triangle with the orthocenter
and circumcircle
Denote
any line containing point
Let and
be the reflections of
in the edges
and
respectively.
Prove that lines and
are concurrent and the point of concurrence lies on
Proof
Let and
be the crosspoints of
with
and
respectively.
WLOG
Let
and
be the points symmetric to
with respect
and
respectively.
Therefore
Let be the crosspoint of
and
is cyclic
Similarly is cyclic
the crosspoint of
and
is point
Usually the point is called the anti-Steiner point of the
with respect to
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Ortholine
Let four lines made four triangles of a complete quadrilateral.
In the diagram these are
Let points and
be the orthocenters of
and
respectively.
Prove that points and
are collinear.
Proof
Let be Miquel point of a complete quadrilateral.
Line is the line which contain
Simson lines of
triangles.
Using homothety centered at with ratio
we get
coinciding Stainer lines which contain points
and
.
Proof 2
Points and
are collinear.
According the Claim of parallel lines, points and
are collinear.
Similarly points and
are collinear as desired.
Claim of parallel lines
Let points and
be collinear.
Let points be such that
Prove that points and
are collinear.
Proof
Let
The segments and
are corresponding segments in similar triangles.
Therefore
and
are collinear.
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Shatunov-Tokarev line
Let the quadrilateral be given (
is not cyclic). Let points
and
be the midpoints of
and
respectively. Let points
and
be such points that
a) Prove that
b) Prove that the point lies on the line
iff
Proof
a) Let be the circle centered at
with radius
Let
be the circle centered at
with radius
is the median of
The power of the point with respect to the circle
is
is the median of
The power of the point with respect to the circle
is
Therefore lies on the radical axis of
and
Similarly,
lies on these line.
So the line
is the radical axes of
and
This line is perpendicular to Gauss line which is the line of centers of two circles
and
as desired.
b) is the median of
is the median of
lies on the radical axes of
and
If the point satisfies the equation
then locus of
is the straight line (one can prove it using method of coordinates).
The points and
are satisfies this equation, so this line contain these points as desired.
It is easy to understand that this line is parallel to Steiner line which is the radical axis of the circles centered at and
with radii
and
respectively.
Of course, it is parallel to Simson line.
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