Imtersecting two regular pentagons
by Miquel-point, May 14, 2025, 6:27 PM
The intersection of two congruent regular pentagons is a decagon with sides of
in this order. Prove that
![\[a_1a_3+a_3a_5+a_5a_7+a_7a_9+a_9a_1=a_2a_4+a_4a_6+a_6a_8+a_8a_{10}+a_{10}a_2.\]](//latex.artofproblemsolving.com/9/e/e/9ee73bbdc4b4f2cad2eb3fcfb3dbdf76b6200b4d.png)

![\[a_1a_3+a_3a_5+a_5a_7+a_7a_9+a_9a_1=a_2a_4+a_4a_6+a_6a_8+a_8a_{10}+a_{10}a_2.\]](http://latex.artofproblemsolving.com/9/e/e/9ee73bbdc4b4f2cad2eb3fcfb3dbdf76b6200b4d.png)
D1031 : A general result on polynomial 1
by Dattier, May 14, 2025, 5:14 PM
Nice one
by imnotgoodatmathsorry, May 2, 2025, 2:10 PM
Old hard problem
by ItzsleepyXD, Apr 25, 2025, 4:15 AM
Let
be a triangle and let
be its circumcenter and
its incenter.
Let
be the radical center of its three mixtilinears and let
be the isogonal conjugate of
.
Let
be the Gergonne point of the triangle
.
Prove that line
is parallel with line
.



Let



Let


Prove that line


Easy Geometry
by pokmui9909, Mar 30, 2025, 5:18 AM
Triangle
satisfies
. Let the incenter of triangle
be
, which touches
at
, respectively. Let
be the midpoint of
. Let the circle centered at
passing through
intersect
at
, respecively. Let line
meet
at
, line
meet
at
. Prove that the three lines
are concurrent.



















This post has been edited 1 time. Last edited by pokmui9909, Mar 30, 2025, 5:29 AM
Asymmetric FE
by sman96, Feb 8, 2025, 5:11 PM
monving balls in 2018 boxes
by parmenides51, Sep 6, 2022, 11:50 PM
There are
boxes
,
,
,..,
. The
-th box
contains
balls.
A move consists of the following steps:
a) Choose an integer
greater than
and choose
a multiple of
.
b) Take a ball from each of the consecutive boxes
,
,
and move the
balls to the box
.
With these movements, what is the largest number of balls we can get in the box
?








A move consists of the following steps:
a) Choose an integer




b) Take a ball from each of the consecutive boxes





With these movements, what is the largest number of balls we can get in the box

This post has been edited 1 time. Last edited by parmenides51, Sep 7, 2022, 12:36 AM
Chinese Girls Mathematical Olympiad 2017, Problem 7
by Hermitianism, Aug 16, 2017, 9:29 AM
This is a very classical problem.
Let the
be a cyclic quadrilateral with circumcircle
.Lines
and
intersect at point
,and lines
,
intersect at point
.Circle
is tangent to segments
at points
respectively,and intersects with circle
at points
.Lines
intersect line
at
respectively.Show that
are concyclic.
Let the

















This post has been edited 1 time. Last edited by Hermitianism, Aug 17, 2017, 9:04 AM
acute triangle and its circumcenter and orthocenter
by N.T.TUAN, May 14, 2007, 7:19 PM
Let
be an acute triangle, and let
and
be its circumcenter and orthocenter, respectively. For
, points
and
lie on lines
and
(where
), respectively, such that
is a parallelogram. Prove that
![\[\frac{OQ_{1}}{OP_{1}}+\frac{OQ_{2}}{OP_{2}}+\frac{OQ_{3}}{OP_{3}}\geq 3.\]](//latex.artofproblemsolving.com/b/a/5/ba563336236b6a04fc9ef661760fa1251bfb07d6.png)










![\[\frac{OQ_{1}}{OP_{1}}+\frac{OQ_{2}}{OP_{2}}+\frac{OQ_{3}}{OP_{3}}\geq 3.\]](http://latex.artofproblemsolving.com/b/a/5/ba563336236b6a04fc9ef661760fa1251bfb07d6.png)
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