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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

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[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/list]
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0 replies
jlacosta
May 1, 2025
0 replies
Both a and a+1997 are roots of P, Q(P(x))=1 has no solutions
WakeUp   2
N 20 minutes ago by Rohit-2006
Source: Baltic Way 1997
Let $P$ and $Q$ be polynomials with integer coefficients. Suppose that the integers $a$ and $a+1997$ are roots of $P$, and that $Q(1998)=2000$. Prove that the equation $Q(P(x))=1$ has no integer solutions.
2 replies
WakeUp
Jan 28, 2011
Rohit-2006
20 minutes ago
greatest volume
hzbrl   1
N 23 minutes ago by hzbrl
Source: purple comet
A large sphere with radius 7 contains three smaller balls each with radius 3 . The three balls are each externally tangent to the other two balls and internally tangent to the large sphere. There are four right circular cones that can be inscribed in the large sphere in such a way that the bases of the cones are tangent to all three balls. Of these four cones, the one with the greatest volume has volume $n \pi$. Find $n$.
1 reply
hzbrl
Yesterday at 9:56 AM
hzbrl
23 minutes ago
Gheorghe Țițeica 2025 Grade 9 P2
AndreiVila   5
N 25 minutes ago by sqing
Source: Gheorghe Țițeica 2025
Let $a,b,c$ be three positive real numbers with $ab+bc+ca=4$. Find the minimum value of the expression $$E(a,b,c)=\frac{a^2+b^2}{ab}+\frac{b^2+c^2}{bc}+\frac{c^2+a^2}{ca}-(a-b)^2.$$
5 replies
AndreiVila
Mar 28, 2025
sqing
25 minutes ago
Geometry Parallel Proof Problem
CatalanThinker   4
N 43 minutes ago by CatalanThinker
Source: No source found, just yet, please share if you find it though :)
Let M be the midpoint of the side BC of triangle ABC. The bisector of the exterior angle of point A intersects the side BC in D. Let the circumcircle of triangle ADM intersect the lines AB and AC in E and F respectively. If the midpoint of EF is N, prove that MN || AD.
I have done some constructions, but still did not quite get to the answer, see diagram attached below
4 replies
CatalanThinker
2 hours ago
CatalanThinker
43 minutes ago
2024 Putnam A1
KevinYang2.71   21
N Yesterday at 10:01 PM by KAME06
Determine all positive integers $n$ for which there exists positive integers $a$, $b$, and $c$ satisfying
\[
2a^n+3b^n=4c^n.
\]
21 replies
KevinYang2.71
Dec 10, 2024
KAME06
Yesterday at 10:01 PM
Miklos Schweitzer 1968_9
ehsan2004   1
N Yesterday at 7:52 PM by pi_quadrat_sechstel
Let $ f(x)$ be a real function such that
\[ \lim_{x \rightarrow +\infty} \frac{f(x)}{e^x}=1\]
and $ |f''(x)|\leq c|f'(x)|$ for all sufficiently large $ x$. Prove that \[ \lim_{x \rightarrow +\infty} \frac{f'(x)}{e^x}=1.\]

P. Erdos
1 reply
ehsan2004
Oct 8, 2008
pi_quadrat_sechstel
Yesterday at 7:52 PM
Putnam 1956 B7
sqrtX   7
N Yesterday at 7:08 PM by bjump
Source: Putnam 1956
The polynomials $P(z)$ and $Q(z)$ with complex coefficients have the same set of numbers for their zeros but possibly different multiplicities. The same is true for the polynomials
$$P(z)+1 \;\; \text{and} \;\; Q(z)+1.$$Prove that $P(z)=Q(z).$
7 replies
sqrtX
Jul 5, 2022
bjump
Yesterday at 7:08 PM
Linear Space Decomposition
Suan_16   1
N Yesterday at 6:09 PM by loup blanc
Let $A$ be a linear transformation on linear space $V$ satisfying:$$A^l=0$$but $$A^{l-1} \neq 0$$, and $V_0$ is the eigensubspace of eigenvalue $0$. Prove that $V$ can be decomposed to $dim V_0$ $A$-cyclic subspace's direct sum.

Click to reveal hidden text
1 reply
Suan_16
Apr 18, 2025
loup blanc
Yesterday at 6:09 PM
Romanian National Olympiad 1997 - Grade 11 - Problem 2
Filipjack   1
N Yesterday at 5:05 PM by loup blanc
Source: Romanian National Olympiad 1997 - Grade 11 - Problem 2
Let $A$ be a square matrix of odd order (at least $3$) whose entries are odd integers. Prove that if $A$ is invertible, then it is not possible for all the minors of the entries of a row to have equal absolute values.
1 reply
Filipjack
Apr 6, 2025
loup blanc
Yesterday at 5:05 PM
Serious qustion
Thayaden   2
N Yesterday at 4:54 PM by ReticulatedPython
Let $F_n$ be then $n$-th fibbiance number. As $n$ gets bigger and bigger, we have,
$$\frac{F_{n+1}}{F_n}\approx\varphi,$$my question is dose,
$$\lim_{n\rightarrow \infty}\frac{F_{n+1}}{F_n}=\varphi.$$My reservations about this is that $\varphi\in\mathbb{R}\setminus\mathbb{Q}$ and $F_n\in\mathbb{Z}^+$ so $\frac{F_{n+1}}{F_n}\in\mathbb{Q}$. So, if the limit holds, does that mean that if $S$ is a set and $P$ is a set, for each $s\in S$ that $s\not\in P$ we can have, for $\text{Range}(f)=S$ we can have,
$$\lim_{x\rightarrow n}f(x)\in P,$$for some $n$?
2 replies
Thayaden
Yesterday at 4:40 PM
ReticulatedPython
Yesterday at 4:54 PM
Putnam 2010 B5
Kent Merryfield   25
N Yesterday at 2:59 PM by Rohit-2006
Is there a strictly increasing function $f:\mathbb{R}\to\mathbb{R}$ such that $f'(x)=f(f(x))$ for all $x?$
25 replies
Kent Merryfield
Dec 6, 2010
Rohit-2006
Yesterday at 2:59 PM
Determinant problem
Entrepreneur   3
N Yesterday at 2:49 PM by Entrepreneur
Source: Hall & Knight
If a determinant is of $n^{\text{th}}$ order, and if the constituents of its first, second, ..., $n^{\text{th}}$ rows are the first $n$ figurate numbers of the first, second, ..., $n^{\text{th}}$ orders respectively, show that it's value is $1.$
3 replies
Entrepreneur
May 5, 2025
Entrepreneur
Yesterday at 2:49 PM
AB=BA if A-nilpotent
KevinDB17   2
N Yesterday at 1:01 PM by loup blanc
Let A,B 2 complex n*n matrices such that AB+I=A+B+BA
If A is nilpotent prove that AB=BA
2 replies
KevinDB17
Mar 30, 2025
loup blanc
Yesterday at 1:01 PM
Putnam 2016 A1
Kent Merryfield   16
N Yesterday at 10:49 AM by sangsidhya
Find the smallest positive integer $j$ such that for every polynomial $p(x)$ with integer coefficients and for every integer $k,$ the integer
\[p^{(j)}(k)=\left. \frac{d^j}{dx^j}p(x) \right|_{x=k}\](the $j$-th derivative of $p(x)$ at $k$) is divisible by $2016.$
16 replies
Kent Merryfield
Dec 4, 2016
sangsidhya
Yesterday at 10:49 AM
VMO 2022 problem 3 day 1
799786   4
N Jul 12, 2024 by khanhnx
Source: Vietnam Mathematical Olympiad 2022 problem 3 day 1
Let $ABC$ be a triangle. Point $E,F$ moves on the opposite ray of $BA,CA$ such that $BF=CE$. Let $M,N$ be the midpoint of $BE,CF$. $BF$ cuts $CE$ at $D$
a) Suppost that $I$ is the circumcenter of $(DBE)$ and $J$ is the circumcenter of $(DCF)$, Prove that $MN \parallel IJ$
b) Let $K$ be the midpoint of $MN$ and $H$ be the orthocenter of triangle $AEF$. Prove that when $E$ varies on the opposite ray of $BA$, $HK$ go through a fixed point
4 replies
799786
Mar 4, 2022
khanhnx
Jul 12, 2024
VMO 2022 problem 3 day 1
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G H BBookmark kLocked kLocked NReply
Source: Vietnam Mathematical Olympiad 2022 problem 3 day 1
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799786
1052 posts
#1 • 1 Y
Y by loveGeometrytothemoon
Let $ABC$ be a triangle. Point $E,F$ moves on the opposite ray of $BA,CA$ such that $BF=CE$. Let $M,N$ be the midpoint of $BE,CF$. $BF$ cuts $CE$ at $D$
a) Suppost that $I$ is the circumcenter of $(DBE)$ and $J$ is the circumcenter of $(DCF)$, Prove that $MN \parallel IJ$
b) Let $K$ be the midpoint of $MN$ and $H$ be the orthocenter of triangle $AEF$. Prove that when $E$ varies on the opposite ray of $BA$, $HK$ go through a fixed point
This post has been edited 1 time. Last edited by 799786, Mar 4, 2022, 10:31 AM
Reason: typo
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799786
1052 posts
#2
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The idea of this problem is complete quadrilateral
a) Use similar triangle and a bit of angle chasing
b) note that $HK$ is the Steiner line of quadrilateral $BCFE$
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NTstrucker
164 posts
#3
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a) Let $MI$ intersects $NJ$ at $P$. Note that $MI$ and $NJ$ are perpendicular bisectors of $BE$ and $CF$, we have $PB=PE$ and $PC=PF$. Combining with $BF=CE$ we get $PEC \cong PBF$. Hence, $PEB \sim PCF$ and $(I,J),(M,N)$ are corresponding points. So $\tfrac{PI}{PM}=\tfrac{PJ}{PN}$ and therefore $MN$ is parallel to $IJ$.

b) We claim that $HK$ passes through $T$, the orthocenter of $ABC$.
Let $U,V$ be the midpoints of $BF$ and $CE$. Observe that $K=\tfrac{M+N}{2}=\tfrac{1}{2} \left( \tfrac{B+E}{2} +\tfrac{C+F}{2} \right)=\tfrac{1}{2} \left( \tfrac{B+F}{2} +\tfrac{C+E}{2} \right)=\tfrac{U+V}{2}$, so $K$ is the midpoint of $UV$. Also note that $(CE)$ and $(BF)$ have the same radius, so $K$ lies on the radical axis of $(CE)$ and $(BF)$.

As $H,T$ are orthocenter of $AEF$ and $ABC$, it's easy to prove that $H,T$ lie on the radical axis of $(CE)$ and $(BF)$ (by introducing the feet of altitudes). So $H,T,K$ are collinear.

Remark. $P$ also lies on the radical axis, because $PEC \cong PBF$ implies $PU=PV$.
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trinhquockhanh
522 posts
#4
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https://i.ibb.co/gd1XBnX/2022-VMO-P3.png
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khanhnx
1618 posts
#5
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a) Let $S$ be second intersection of $(DBE)$ and $(DCF)$. We have $\angle{SFD} = \angle{SCD}$ and $\angle{SED} = \angle{SBD}$. Combine with $BF = CE,$ we have $\triangle SBF = \triangle SEC$. Hence $SB = SE$ and $SC = SF$. From this, we have $S, I, M$ are collinear and $S, J, N$ are collinear. We also have $\angle{SBE} = \angle{SDE} = \angle{SFC} = \angle{SCF} = \angle{SDF} = \angle{SEB}$. Then $\triangle SBE \cup I \cup M \sim \triangle SFC \cup J \cup N$. So $\dfrac{SI}{SM} = \dfrac{SJ}{SN}$ or $IJ \parallel MN$.
b) Suppose that $P, Q$ are midpoints of $BF, CE$. Then it's easy to see that $MPNQ$ is parallelogram. So $K$ is midpoint of $EF$. But $BF = CE$ then $K$ lies on radical axis of $\bigodot(BF)$ and $\bigodot(CE)$. Hence $HK$ is Steiner line of completed quadrilateral formed by $BC, CE, EF, FB$. This means $HK$ passes through orthocenter of $\triangle ABC,$ which is a fixed point.
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