Geometry
by AlexCenteno2007, May 15, 2025, 4:42 AM
Let ABC be an acute triangle. The altitudes from B and C intersect the sides AC and AB at E and F, respectively. The internal bisector of ∠A intersects BE and CF at T and S, respectively. The circles with diameters AT and AS intersect the circumcircle of ABC at X and Y, respectively. Prove that XY, EF, and BC meet at the exsimilicenter of BTX and CSY
Inspired by xytunghoanh
by sqing, May 15, 2025, 3:04 AM
Based on IMO 2024 P2
by Miquel-point, May 14, 2025, 6:15 PM
Prove that for any positive integers
,
,
and
there exists infinitely many positive integers
for which
and
are not relatively primes.
Proposed by Géza Kós







Proposed by Géza Kós
Nice one
by imnotgoodatmathsorry, May 2, 2025, 2:10 PM
functional equation
by hanzo.ei, Apr 6, 2025, 6:08 PM
Equal segments in a cyclic quadrilateral
by a_507_bc, Jul 29, 2023, 12:15 PM
Consider a cyclic quadrilateral
in which
and
. Let
be a point on the side
and
a point on the line
such that
. Prove that
.









egmo 2018 p4
by microsoft_office_word, Apr 12, 2018, 11:02 AM
A domino is a
or
tile.
Let
be an integer. Dominoes are placed on an
board in such a way that each domino covers exactly two cells of the board, and dominoes do not overlap. The value of a row or column is the number of dominoes that cover at least one cell of this row or column. The configuration is called balanced if there exists some
such that each row and each column has a value of
. Prove that a balanced configuration exists for every
, and find the minimum number of dominoes needed in such a configuration.


Let





This post has been edited 3 times. Last edited by microsoft_office_word, Feb 18, 2020, 9:47 PM
integer functional equation
by ABCDE, Jul 7, 2016, 7:52 PM
Determine all functions
with the property that
holds for all
.

![\[f(x-f(y))=f(f(x))-f(y)-1\]](http://latex.artofproblemsolving.com/f/2/5/f25cc1e8ae0be1fd02b347fd94be4fab88af1d46.png)

Tangents to a cyclic quadrilateral
by v_Enhance, Jul 23, 2013, 1:32 AM
Let
be a cyclic quadrilateral inscribed in circle
whose diagonals meet at
. Lines
and
meet at
. Segment
intersects
at
. Lines
and
meet at
, and lines
and
meet at
. Prove that
and
concur with the tangent to
at
.
Proposed by Allen Liu



















Proposed by Allen Liu
"Where wisdom and valor fail, all that remains is faith. . . And it can overcome all." -Toa Mata Tahu
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