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k a June Highlights and 2025 AoPS Online Class Information
jlacosta   0
Today at 3:57 PM
Congratulations to all the mathletes who competed at National MATHCOUNTS! If you missed the exciting Countdown Round, you can watch the video at this link. Are you interested in training for MATHCOUNTS or AMC 10 contests? How would you like to train for these math competitions in half the time? We have accelerated sections which meet twice per week instead of once starting on July 8th (7:30pm ET). These sections fill quickly so enroll today!

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0 replies
jlacosta
Today at 3:57 PM
0 replies
IMO Genre Predictions
ohiorizzler1434   78
N 3 minutes ago by ohiorizzler1434
Everybody, with IMO upcoming, what are you predictions for the problem genres?


Personally I predict: predict
78 replies
ohiorizzler1434
May 3, 2025
ohiorizzler1434
3 minutes ago
The Return of Triangle Geometry
peace09   12
N 10 minutes ago by peace09
Source: 2023 ISL A7
Let $N$ be a positive integer. Prove that there exist three permutations $a_1,\dots,a_N$, $b_1,\dots,b_N$, and $c_1,\dots,c_N$ of $1,\dots,N$ such that \[\left|\sqrt{a_k}+\sqrt{b_k}+\sqrt{c_k}-2\sqrt{N}\right|<2023\]for every $k=1,2,\dots,N$.
12 replies
peace09
Jul 17, 2024
peace09
10 minutes ago
Find Triples of Integers
termas   40
N 15 minutes ago by monval
Source: IMO 2015 problem 2
Find all positive integers $(a,b,c)$ such that
$$ab-c,\quad bc-a,\quad ca-b$$are all powers of $2$.

Proposed by Serbia
40 replies
termas
Jul 10, 2015
monval
15 minutes ago
AT // BC wanted
parmenides51   106
N 23 minutes ago by happypi31415
Source: IMO 2019 SL G1
Let $ABC$ be a triangle. Circle $\Gamma$ passes through $A$, meets segments $AB$ and $AC$ again at points $D$ and $E$ respectively, and intersects segment $BC$ at $F$ and $G$ such that $F$ lies between $B$ and $G$. The tangent to circle $BDF$ at $F$ and the tangent to circle $CEG$ at $G$ meet at point $T$. Suppose that points $A$ and $T$ are distinct. Prove that line $AT$ is parallel to $BC$.

(Nigeria)
106 replies
parmenides51
Sep 22, 2020
happypi31415
23 minutes ago
No more topics!
Romanian National Olympiad 2012 - Grade IX - problem 1
Mateescu Constantin   10
N May 29, 2014 by Sardor
The altitude $[BH]$ dropped onto the hypotenuse of a triangle $ABC$ intersects the bisectors $[AD]$ and $[CE]$ at $Q$ and $P$ respectively. Prove that the line passing through the midpoints of the segments $[QD]$ and $[PE]$ is parallel to the line $AC$ .
10 replies
Mateescu Constantin
Apr 5, 2012
Sardor
May 29, 2014
Romanian National Olympiad 2012 - Grade IX - problem 1
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Mateescu Constantin
1842 posts
#1 • 3 Y
Y by Adventure10, Mango247, and 1 other user
The altitude $[BH]$ dropped onto the hypotenuse of a triangle $ABC$ intersects the bisectors $[AD]$ and $[CE]$ at $Q$ and $P$ respectively. Prove that the line passing through the midpoints of the segments $[QD]$ and $[PE]$ is parallel to the line $AC$ .
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jayme
9803 posts
#2 • 1 Y
Y by Adventure10
Dear Mathlinkers,
this problem being an adaptation of a de Longchamps result, you can see a kind of synthetic proof on

http://perso.orange.fr/jl.ayme vol. 5 ...de Longchamps.... p. 22.

Sincerely
jean-Louis
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Dranzer
154 posts
#3 • 8 Y
Y by yugrey, Adventure10, and 6 other users
Instead of linking to an external website written in a language not so well known to others and with faulty, dumb,ridiculous and excruciatingly funny translations by Chrome and Google can you post that in English?
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jatin
547 posts
#4 • 6 Y
Y by Adventure10, Mango247, and 4 other users
I wholeheartedly agree, and I have posted this before.

Dear Jayme, your articles will get a much larger audience and attention if you post them in English. I would dearly like to read your articles, as I'm sure many others would. So could you please make an effort to write them in English?
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mavropnevma
15142 posts
#5 • 8 Y
Y by WakeUp, jatin, Adventure10, Mango247, and 4 other users
He is French, he writes in French, and he is posting on a French website. Maybe you all can make an effort, and try to understand it; the effect will be not only that you will see and learn beautiful geometry, but also improve your foreign language(s) skills. This was done at large in Romania in the 50's, 60's and 70's, when all good mathematics was to be found just in Russian books, written in Russian language, and the gap between Romanian and Russian is much larger than that between English and French (just to mention a different alphabet).
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sunken rock
4402 posts
#6 • 3 Y
Y by Adventure10, Mango247, and 1 other user
Well, see that triangles $\triangle BEP, \triangle BQD$ are isosceles, hence if $M, N$ are the midpoints of $[PE]$, respectively $[QD]$, we have $BM\bot CE, BN\bot AD$, $\angle MBP=\frac{\widehat C}{2}, \angle NBQ=\frac{\widehat A}{2}$, i.e. $BMIN$ is cyclic, $I$ being the incenter. From $\angle DBI=\angle MBN=45^\circ\implies \angle IBN = \angle MBP = \frac{\widehat C}{2}$. From $BMIN$ we get $\angle NMI=\angle NBI=\angle MBP=\angle ACE = \frac{\widehat C}{2}$, or $MN\parallel AC$.

Best regards,
sunken rock
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jatin
547 posts
#7 • 4 Y
Y by tudor129, Adventure10, Mango247, and 1 other user
@mavropnevma: Yes, we could do all that, but wouldn't it be much more convenient if the author writes in English itself (specially when he knows English well)? I don't see your point here.
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sunken rock
4402 posts
#8 • 4 Y
Y by jatin, Adventure10, and 2 other users
@jatin: No, it isn't, he does not write specially for us, but for his community; he only shares his work with us. If you really want to read it when you do not know French, you may use Google translator or a ... teacher!

I heard a legend, the late Bobby Fisher learned Russian to read the Russian chess magazines and it has been worth of.

Best regards,
sunken rock
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jatin
547 posts
#9 • 3 Y
Y by Adventure10, Mango247, and 1 other user
sunken rock wrote:
@jatin: No, it isn't, he does not write specially for us, but for his community; he only shares his work with us.
Ah, I didn't know that. Well, if that is the case, yes, all I can do is try to learn some French. :)

I thank both skytin and mavropnevma for sharing their experience.
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SmartClown
82 posts
#10 • 2 Y
Y by Adventure10, Mango247
The problem is nice for doing analytic geometry.We put $B(0,0)$ and $A(0,a)$ and $C(1,0)$.After that it is just simple calculations and not much thinking.
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Sardor
801 posts
#11 • 2 Y
Y by Adventure10, Mango247
See here http://www.artofproblemsolving.com/Forum/viewtopic.php?p=3068344&sid=754f63f6fb3a9b1ab9bbcb133e9e1ad9#p3068344
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