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jlacosta   0
May 1, 2025
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0 replies
jlacosta
May 1, 2025
0 replies
A number theory problem
super1978   0
8 minutes ago
Source: Somewhere
Let $a,b,n$ be positive integers such that $\sqrt[n]{a}+\sqrt[n]{b}$ is an integer. Prove that $a,b$ are both the $n$th power of $2$ positive integers.
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super1978
8 minutes ago
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Nuran2010   3
N 16 minutes ago by Nuran2010
Source: Azerbaijan Al-Khwarizmi IJMO TST 2025
The numbers $\frac{50}{1},\frac{50}{2},...\frac{50}{97},\frac{50}{98}$ are written on the board.In each step,two random numbers $a$ and $b$ are chosen and deleted.Then,the number $2ab-a-b+1$ is written instead.What will be the number remained on the board after the last step.
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Nuran2010
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Nuran2010
16 minutes ago
A irreducible polynomial
super1978   0
18 minutes ago
Source: Somewhere
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super1978
18 minutes ago
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(2^n + 1)/n^2 is an integer (IMO 1990 Problem 3)
orl   107
N 28 minutes ago by Rayvhs
Source: IMO 1990, Day 1, Problem 3, IMO ShortList 1990, Problem 23 (ROM 5)
Determine all integers $ n > 1$ such that
\[ \frac {2^n + 1}{n^2}
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orl
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N 2 hours ago by ZeroAlephZeta
Source: ISI UGB 2025 P1
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ZeroAlephZeta
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Silver08   11
N 3 hours ago by quasar_lord
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Silver08
May 9, 2025
quasar_lord
3 hours ago
nice integral
Martin.s   1
N 4 hours ago by ysharifi
$$ \int_{0}^{\infty} \ln(2t) \ln(\tanh t) \, dt $$
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Martin.s
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ysharifi
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Dattier   2
N 6 hours ago by ysharifi
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Let $p>3$ a prime number, with $H \subset M_p(\mathbb R), \dim(H)\geq 2$ and $H-\{0\} \subset GL_p(\mathbb R)$, $H$ vector space.

Is it true that $H-\{0\}$ is a group?
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Dattier
Yesterday at 1:49 PM
ysharifi
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Mathematical expectation 1
Tricky123   0
Today at 9:51 AM
X is continuous random variable having spectrum
$(-\infty,\infty) $ and the distribution function is $F(x)$ then
$E(X)=\int_{0}^{\infty}(1-F(x)-F(-x))dx$ and find the expression of $V(x)$

Ans:- $V(x)=\int_{0}^{\infty}(2x(1-F(x)+F(-x))dx-m^{2}$

How to solve help me
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Tricky123
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fermion13pi   1
N Today at 8:11 AM by Svyatoslav
Source: Apostol, vol 2
Evaluate the double integral by converting to polar coordinates:

\[
\int_0^1 \int_{x^2}^x (x^2 + y^2)^{-1/2} \, dy \, dx
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Change the order of integration and then convert to polar coordinates.

1 reply
fermion13pi
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Hey integration fans. I decided to collate some of my favourite and most evil integrals I've written into one big integration bee problem set. I've been entering integration bees since 2017 and I've been really getting hands on with the writing side of things over the last couple of years. I hope you'll enjoy!
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N Today at 5:26 AM by parkjungmin
It's about the Japanese Olympiad

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If there are people who are good at math

Please help me.
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parkjungmin
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parkjungmin
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Japanese high school Olympiad.
parkjungmin   0
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It's about the Japanese high school Olympiad.

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parkjungmin
Today at 5:25 AM
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Iranian Geometry Olympiad (2)
MRF2017   12
N Jul 12, 2024 by Rounak_iitr
Source: Advanced level,P2
In acute-angled triangle $ABC$, altitude of $A$ meets $BC$ at $D$, and $M$ is midpoint of $AC$. Suppose that $X$ is a point such that $\measuredangle AXB = \measuredangle DXM =90^\circ$ (assume that $X$ and $C$ lie on opposite sides of the line $BM$). Show that $\measuredangle XMB = 2\measuredangle MBC$.Proposed by Davood Vakili
12 replies
MRF2017
Sep 13, 2016
Rounak_iitr
Jul 12, 2024
Iranian Geometry Olympiad (2)
G H J
G H BBookmark kLocked kLocked NReply
Source: Advanced level,P2
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MRF2017
237 posts
#1 • 3 Y
Y by Davi-8191, Adventure10, Rounak_iitr
In acute-angled triangle $ABC$, altitude of $A$ meets $BC$ at $D$, and $M$ is midpoint of $AC$. Suppose that $X$ is a point such that $\measuredangle AXB = \measuredangle DXM =90^\circ$ (assume that $X$ and $C$ lie on opposite sides of the line $BM$). Show that $\measuredangle XMB = 2\measuredangle MBC$.Proposed by Davood Vakili
This post has been edited 1 time. Last edited by nsato, Oct 5, 2019, 1:57 PM
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Math_CYCR
431 posts
#2 • 2 Y
Y by Coxivai, Adventure10
Easily $\angle BAD= \angle BXD$. And $\angle AMX+ \angle ABX= \angle MDC= \angle DMB+ \angle DBM (\star )$

Law of sines in $\triangle AXM$:

$$\frac{AX}{AM} = \frac{ \sin \angle AMX}{ \sin \angle BAD}$$
Law of sines in $\triangle ABX$:

$$\frac{AB}{AX} = \frac{ \sin 90}{ \sin \angle ABX}$$
Law of sines in $\triangle ABD$:

$$\frac{BD}{AB} = \frac{ \sin \angle BAD}{ \sin 90}$$
Law of sines in $\triangle BDM$:

$$\frac{DM}{BD} = \frac{ \sin \angle DBM}{ \sin \angle DMB}$$
Multiplying the four equations we get:

$ \frac{ \sin \angle ABX}{ \sin \angle AMX} = \frac{ \sin \angle DBM}{ \sin \angle DMB}$ $(\star \star )$

By $(\star )$ and $(\star \star )$, Two Equal Angles Lemma we get $\angle AMX= \angle DMB$. The conclusion follows.
This post has been edited 3 times. Last edited by Math_CYCR, Sep 25, 2016, 2:24 PM
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anhtaitran
363 posts
#3 • 2 Y
Y by Adventure10, Mango247
My solution:Let XM cut (ABD) and BC at T and Y.
We have:TAD=TXD=180-DXM=90.
So AT parallel to BC.
So ATCY is a paralellogram.
So M is the midpoint of TY too.(1)
Because the triangle TBY=90.(2)
So MY=MB.
So XMB=2MBC.
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madmathlover
145 posts
#4 • 4 Y
Y by Reynan, Geronimo_1501, Adventure10, Mango247
Let $N$ be the midpont of $AB$.Obviously $A,X,D,B$ are concyclic.Now,
$-\measuredangle BXM=\measuredangle DXA=\measuredangle DBA=-\measuredangle BNM$.

So,$B,N,X,M$ are also concyclic.

Now,since $NA=NB=NX$,so,$NM$ bisects $\angle XMB$.As $MN \parallel BC$,we are done.
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Re1gnover
139 posts
#5 • 3 Y
Y by I.owais, Adventure10, Mango247
Let $BM$ meets $(AB)$ at $Y$ and $MX$ meets $(AB)$ at $Z$. Then we have $XY || BZ \implies XY\perp BC$ at $T$ and $MX=MY$.
So we get that $\angle XMY=180^\circ-2\angle MYX=180^\circ-2\angle BNT=2\angle MBC.$
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WizardMath
2487 posts
#6 • 1 Y
Y by Adventure10
Let $Z$ be the midpoint of $AB$. $BZM= \pi - DBA= DXA = BXM$ and due to the condition on the position of X, $BZXM$ is cyclic. Now since $Z$ is the center of $(AB)$, it is the midpoint of $\overarc{BX}$ of the previously mentioned circle. Now since $MZ || BC$ we get that the bisector of $\angle XMB$ is parallel to $BC$ which completes the solution.
Click to reveal hidden text
This post has been edited 1 time. Last edited by WizardMath, Sep 15, 2016, 4:03 AM
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Ankoganit
3070 posts
#7 • 3 Y
Y by Adventure10, Mango247, Rounak_iitr
[asy]size(8cm);
pair A=(3,6),B=(0,0),C=(10,0),D,M,Nn,X,Y;
D=foot(A,B,C);M=(A+C)/2;Nn=(A+B)/2;Y=2*Nn-D;X=foot(D,M,Y);
draw(circumcircle(B,D,A)^^circumcircle(D,X,M),cyan+green);
D(MP("A",A,N)--MP("N",Nn,W)--MP("B",B,S)--MP("D",D,S)--MP("C",C,S)--MP("M",M,E)--A);
D(M--MP("X",X,dir(275)*2)--MP("Y",Y,N),heavymagenta);
draw(D--Nn--Y--A--D--M--Nn^^D--X--A^^B--X^^Y--B--M,heavymagenta);
dot(A^^B^^C^^D^^X^^Y^^M^^Nn);
[/asy]
Let $MX$ meet $\odot (AB)$ again at $Y$, and let $N$ be the midpoint of $AB$ (i.e., the center of the circle with diameter). Then $$\angle YXD=\pi-\angle DXM=\pi-\frac{\pi}{2}=\frac{\pi}{2},$$so $Y$ is the antipode of $D$ in $\odot (AB)$, so $AYBD$ is a rectangle. Since $MN$ is clearly the perpendicular bisector of $AD$, $MY$ and $MB$ are symmetric wrt $MN$, so $$\angle XMN=\angle NMB\implies \angle XMB=\angle XMN+\angle NMB=2\angle NMB=2\angle MBC.\;\blacksquare$$
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rafaello
1079 posts
#8
Y by
Let $N$ be the midpoint of $\overline{AB}$ and $P$ be the midpoint of $\overline{AD}$. Observe that $P$ lies on $(XDM)$ and on $\overline{MN}$.
Firstly, note that $BNXM$ is cyclic quadrilateral as \begin{align*}
\measuredangle NBX =\measuredangle PDX=\measuredangle PMX=\measuredangle NMX.
\end{align*}Now, note that $\measuredangle NBX=\measuredangle BXN=\measuredangle BMN=\measuredangle  MBC$, which means that $\overline{BX},\overline{BM}$ are isogonal wrt $\angle ABC$. Thus indeed $\measuredangle XMB=\measuredangle XMN+\measuredangle NMB=\measuredangle XBN+\measuredangle MBC=2\measuredangle MBC$. $\blacksquare$
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X.Allaberdiyev
103 posts
#9 • 1 Y
Y by Halykov
Let the tangents at $A$ and $C$ to $(A B C)$ meet at point $K$. From $(A X D B)$ cyclic, we have $180 - \angle AXM=\angle BXD=\angle BAD$ and we can easily see that $\angle AKM=\angle BAD$, from these we get that $(A X M K)$ cyclic. Then we have $90=\angle AMK=\angle AXK$, implying that $B$, $X$ and $K$ are collinear. Since $BK$ is symmedian of $\angle ABC$, we have $\angle ABX=\angle MBD$. And we know that $90+\angle DBT=\angle BDX=90+\angle ADX=90+\angle ABX$, then $\angle DBT=\angle ABX$ (then $\angle DBT=\angle ABX=\angle MBD$). From $MX//BT$ we have $\angle XMB=\angle MBT=2\angle MBD$ which completes the solution.
This post has been edited 6 times. Last edited by X.Allaberdiyev, Aug 17, 2023, 6:55 PM
Reason: Latex
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Halykov
26 posts
#10 • 1 Y
Y by Halykovmathclub
Halykov wrote:
X.Allaberdiyev wrote:
Let the tangents at $A$ and $C$ to $(ABC)$ meet at point $K$. From $AXDB$ cyclic, we have 180 - ∠AXM=∠BXD∠=∠BAD and we can easily see that ∠AKM=∠BAD, from these we get that $AXMK$ cyclic. Then we have 90=∠AMK=∠AXK, implying that $B, X, K$ are collinear. Since $BK$ is symmedian of ∠ABC, we have ∠ABX=∠MBD. And we know that 90+∠DBT=∠BDX=90+∠ADX=90+∠ABX --> DBT=∠ABX (then ∠DBT=∠ABX=∠MBD). From $MX//BT$ we have ∠XMB=∠MBT=2∠MBD which completes the solution.

Latex form of this solution
This post has been edited 2 times. Last edited by Halykov, Jul 30, 2023, 6:49 PM
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lian_the_noob12
173 posts
#13
Y by
$\color{red} \textbf{Geo Marabot Solve 5}$

Let, $N$ be the mid point of $AB$ and $AD\cap MN \equiv D'.$ $\angle NMB=\angle MBC.$ Hence we need to show $\angle XMN=\angle MBC$
We have, $A,B,D,X$ concyclic and $D,D',X,M$ concyclic. So,
$$\angle XMN=\angle XDD'=\angle XDA=\angle XBA=\angle XBN \implies B,N,X,M$$cyclic

$$\implies \angle XBN=\angle BXN=\angle BMN=\angle MBC \blacksquare$$
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giannis2006
45 posts
#14
Y by
Let $N$ be the midpoint of $AB$. We have that $\angle AXB = 90 = \angle ADB$, hence $A,X,D,B$ are conclycic with diameter $AB$, so $N$ is the center of $(AXDB)$, i.e. $NA=NX=ND=NB$. Also, $MN \parallel BC => MN \perp AD$ and $\angle DXM = 90 => XM \perp DX$, hence $\angle XMN = \angle XDA$ as their sides are perpendicular.
From the cyclic $AXDB$ we get that $ \angle NBX = \angle ABX = \angle ADX = \angle XDA = \angle XMN => BNXM$ is cyclic and, using that $NB=NX$, we conclude that $NM$ bisects $\angle XMB$. Hence we get that $\angle XMB = 2 \angle NMB = 2 \angle MBC$, where the last equalith holds because $MN \parallel BC$.
Attachments:
This post has been edited 1 time. Last edited by giannis2006, Jul 5, 2024, 6:10 PM
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Rounak_iitr
456 posts
#16
Y by
[asy]
 /* Geogebra to Asymptote conversion, documentation at artofproblemsolving.com/Wiki go to User:Azjps/geogebra */
import graph; size(13cm); 
real labelscalefactor = 0.5; /* changes label-to-point distance */
pen dps = linewidth(0.7) + fontsize(10); defaultpen(dps); /* default pen style */ 
pen dotstyle = black; /* point style */ 
real xmin = -17.24248, xmax = 19.83192, ymin = -13.56324, ymax = 8.02316;  /* image dimensions */

 /* draw figures */
draw((-3.2,6.98)--(-9,-5.7), linewidth(0.8) + red); 
draw((-9,-5.7)--(9.86,-5.52), linewidth(0.8) + red); 
draw((-3.2,6.98)--(9.86,-5.52), linewidth(0.8) + red); 
draw((-3.2,6.98)--(-3.421008752341651,-5.646754060202625), linewidth(0.8)); 
draw((-3.2,6.98)--(0.574,2.066), linewidth(0.8)); 
draw((0.574,2.066)--(-9,-5.7), linewidth(0.8)); 
draw((-3.421008752341651,-5.646754060202625)--(0.574,2.066), linewidth(0.8)); 
draw((0.574,2.066)--(3.33,0.73), linewidth(0.8)); 
draw((-3.421008752341651,-5.646754060202625)--(3.33,0.73), linewidth(0.8)); 
draw((-6.1,0.64)--(3.33,0.73), linewidth(0.8)); 
draw((-6.1,0.64)--(0.574,2.066), linewidth(0.8)); 
draw((-9,-5.7)--(3.33,0.73), linewidth(0.8)); 
draw(circle((-6.271508027994867,0.7184500443509642), 6.974322147214405), linewidth(0.8) + blue); 
draw(circle((-1.327242851760632,-5.366665643302623), 7.671977772810744), linewidth(0.8) + blue); 
 /* dots and labels */
dot((-3.2,6.98),dotstyle); 
label("$A$", (-3.10968,7.22456), NE * labelscalefactor); 
dot((-9,-5.7),dotstyle); 
label("$B$", (-9.32908,-6.15804), NE * labelscalefactor); 
dot((9.86,-5.52),dotstyle); 
label("$C$", (9.95832,-5.28684), NE * labelscalefactor); 
dot((-3.421008752341651,-5.646754060202625),dotstyle); 
label("$D$", (-3.73888,-6.23064), NE * labelscalefactor); 
dot((3.33,0.73),linewidth(4pt) + dotstyle); 
label("$M$", (3.42432,0.93256), NE * labelscalefactor); 
dot((0.574,2.066),dotstyle); 
label("$X$", (0.66552,2.31196), NE * labelscalefactor); 
dot((-6.1,0.64),linewidth(4pt) + dotstyle); 
label("$N$", (-6.64288,0.69056), NE * labelscalefactor); 
clip((xmin,ymin)--(xmin,ymax)--(xmax,ymax)--(xmax,ymin)--cycle); 
 /* end of picture */
[/asy]

$\color{red}\textbf{Claim:-}$ $\angle XMB=2 \angle MBC.$

$\color{blue}\textbf{Proof:-}$ Let the midpoint of $AB$ is $N.$ From this we get, $A,B,D,X$ are cyclic, Since, $AD\perp BC\implies\angle AXB=\angle ADB=90^o.$ Now Since, $MN\parallel BC\implies \angle BMN=\angle MBC$ also we get, $\angle BNM+\angle ABC=180^o\implies \boxed{\angle BNM=180^o-\angle ABC.}$
Now We claim that $MN$ bisects $\angle XMB.$

Since, $A,B,D,X$ are cyclic we get, $\angle BXD=\angle DAB=90^o-\angle ABC.$ Next we claim that the circle through $A,B,D,X$ has center at $N$ and $AB$ is diameter.
Its very obvious since, $AB$ subtends $90^o$ at $D$ and $X\implies AN=NX=BN.$
Now in triangle $BNX\implies NX=NB\implies\angle NBX=\angle NXB.$ Now we also see that $B,N,X,M$ are cyclic. Since, $\angle BNM=\angle BXM=180^o-\angle ABC.$ Now in Cyclic Quad. $B,M,X,N$ we get, $\angle NXB=\angle NMX\implies \boxed{\angle XMB=2\angle MBC.}$
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