too much tangencies these days...
by kamatadu, Jan 20, 2023, 7:18 PM
Let
be a circle and
be circles internally tangent to
at
and
. Assume that
and
are also externally tangent at point
. Prove that the line through
perpendicular to
meets line
on
.












Rectangle EFGH in incircle, prove that QIM = 90
by v_Enhance, Jul 18, 2014, 7:48 PM
Let
be a triangle with incenter
, and suppose the incircle is tangent to
and
at
and
. Denote by
and
the reflections of
and
over
. Let
be the intersection of
with
, and let
be the midpoint of
. Prove that
and
are perpendicular.


















IMO Shortlist 2011, G1
by WakeUp, Jul 13, 2012, 11:30 AM
Let
be an acute triangle. Let
be a circle whose centre
lies on the side
. Suppose that
is tangent to
at
and
at
. Suppose also that the circumcentre
of triangle
lies on the shorter arc
of
. Prove that the circumcircle of
and
meet at two points.
Proposed by Härmel Nestra, Estonia















Proposed by Härmel Nestra, Estonia
Chords and tangent circles
by math154, Jul 2, 2012, 3:13 AM
Circles
and
are internally tangent at point
. Chord
of
is tangent to
at
, where
is the midpoint of
. Another circle,
is tangent to
and
at
and
respectively. Rays
and
meet at
. If
is the midpoint of major arc
, show that
.
Ray Li.




















Ray Li.
Show that AB/AC=BF/FC
by syk0526, Apr 2, 2012, 3:06 PM
Let
be an acute triangle. Denote by
the foot of the perpendicular line drawn from the point
to the side
, by
the midpoint of
, and by
the orthocenter of
. Let
be the point of intersection of the circumcircle
of the triangle
and the half line
, and
be the point of intersection (other than
) of the line
and the circle
. Prove that
must hold.
(Here we denote
the length of the line segment
.)

















(Here we denote


This post has been edited 5 times. Last edited by syk0526, Apr 4, 2012, 6:48 AM
Lots of perpendiculars; compute HQ/HR
by MellowMelon, Jul 26, 2011, 9:14 PM
In an acute scalene triangle
, points
lie on sides
, respectively, such that
. Altitudes
meet at orthocenter
. Points
and
lie on segment
such that
and
. Lines
and
intersect at point
. Compute
.
Proposed by Zuming Feng















Proposed by Zuming Feng
Perpendicularity
by April, Dec 28, 2008, 4:09 AM
Point
lies inside triangle
such that
and
. Point
is the midpoint of segment
. Point
lies on segment
with
. Prove that
.










This post has been edited 1 time. Last edited by v_Enhance, Jan 25, 2016, 3:51 PM
Reason: \equal -> =
Reason: \equal -> =
incircle with center I of triangle ABC touches the side BC
by orl, Jun 26, 2005, 12:16 PM
Given a triangle
. Let
be the circumcenter of this triangle
. Let
,
,
be the feet of the altitudes of triangle
from the vertices
,
,
, respectively. Denote by
,
,
the midpoints of these altitudes
,
,
, respectively. The incircle of triangle
has center
and touches the sides
,
,
at the points
,
,
, respectively. Prove that the four lines
,
,
and
are concurrent. (When the point
concides with
, we consider the line
as an arbitrary line passing through
.)
































Midpoints of altitudes and concurrent cevians
by darij grinberg, Jul 5, 2004, 1:18 PM
Let
be a triangle. Let
,
,
be the midpoints of its sides
,
,
, and
,
,
the midpoints of the altitudes from
,
,
. Show that the lines
,
, and
meet at one point.
















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