Spieker center
The Spieker center is defined as the center of mass of the perimeter of the triangle. The Spieker center of a is the center of gravity of a homogeneous wire frame in the shape of
The Spieker center is a triangle center and it is listed as the point
Contents
Incenter of medial triangle
Prove that the Spieker center of triangle is the incenter of the medial triangle
of a
Proof
Let's hang up the in the middle of side
Side
is balanced.
Let's replace side with point
(the center of mass of
the midpoint
Denote
the linear density of a homogeneous wire frame.
The mass of point is equal to
the shoulder of the gravity force is
The moment of this force is
Similarly the moment gravity force acting on AB is
Therefore, equilibrium condition is and the center of gravity of a homogeneous wire frame
lies on each bisector of
This point is the incenter of the medial triangle
vladimir.shelomovskii@gmail.com, vvsss
Intersection of three cleavers
Prove that the Spieker center is located at the intersection of the three cleavers of triangle. A cleaver of a triangle is a line segment that bisects the perimeter of the triangle and has one endpoint at the midpoint of one of the three sides.
Proof
We use notation of previous proof. is the segment contains the Spieker center,
WLOG,
Similarly,
So is cleaver.
Therefore, the three cleavers meet at the Spieker center.
vladimir.shelomovskii@gmail.com, vvsss
Radical center of excircles
Prove that the Spieker center of triangle is the radical center of the three excircles.
Proof
Let be given,
be the midpoints of
respectively.
Let be A-excircle, B-excircle, C-excircle centered at
respectively.
Let be the incenter of
Let
be the radical axis of
and
be the radical axis of
and
be the radical axis of
and
respectively.
It is known that the distances from to the tangent points of
is equal to the distances from
to the tangent points of
therefore
lies on the radical axis
of
and
Similarly,
is cleaver. Similarly,
and
are cleavers.
Therefore the radical center of the three excircles coinside with the intersection of the three cleavers of triangle.
vladimir.shelomovskii@gmail.com, vvsss
Nagel line
Let points be the incenter, the centroid and the Spieker center of triangle
respectively. Prove that points
are collinear,
and the barycentric coordinates of S are
The Nagel line is the line on which points
and Nagel point
lie.
Proof
Let be the midpoints of
respectively.
Bisector
is parallel to cleaver
Centroid
divide the median
such that
and points
are collinear.
The barycentric coordinates of
are
The barycentric coordinates of
are
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