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IMO ShortList 2001, number theory problem 4
orl   43
N an hour ago by Zany9998
Source: IMO ShortList 2001, number theory problem 4
Let $p \geq 5$ be a prime number. Prove that there exists an integer $a$ with $1 \leq a \leq p-2$ such that neither $a^{p-1}-1$ nor $(a+1)^{p-1}-1$ is divisible by $p^2$.
43 replies
orl
Sep 30, 2004
Zany9998
an hour ago
Number theory - Iran
soroush.MG   32
N an hour ago by Nobitasolvesproblems1979
Source: Iran MO 2017 - 2nd Round - P1
a) Prove that there doesn't exist sequence $a_1,a_2,a_3,... \in \mathbb{N}$ such that: $\forall i<j: gcd(a_i+j,a_j+i)=1$

b) Let $p$ be an odd prime number. Prove that there exist sequence $a_1,a_2,a_3,... \in \mathbb{N}$ such that: $\forall i<j: p \not | gcd(a_i+j,a_j+i)$
32 replies
soroush.MG
Apr 20, 2017
Nobitasolvesproblems1979
an hour ago
Inspired by my own results
sqing   2
N 2 hours ago by cazanova19921
Source: Own
Let $ a,b,c\geq \frac{1}{2}  . $ Prove that
$$ (a+1)(b+2)(c +1)-15 abc\leq \frac{15}{4}$$$$ (a+1)(b+3)(c +1)-21abc\leq \frac{21}{4}$$$$(a+2)(b+1)(c +2)-25a b c \leq \frac{25}{4}$$$$ (a+2)(b+3)(c +2)-35a b c \leq  \frac{35}{2}$$$$    (a+3)(b+1)(c +3)-49a b c \leq  \frac{49}{4}$$$$ (a+3)(b+2)(c +3)-49a b c \leq \frac{49}{2}$$
2 replies
sqing
3 hours ago
cazanova19921
2 hours ago
Line through incenter tangent to a circle
Kayak   32
N 2 hours ago by L13832
Source: Indian TST D1 P1
In an acute angled triangle $ABC$ with $AB < AC$, let $I$ denote the incenter and $M$ the midpoint of side $BC$. The line through $A$ perpendicular to $AI$ intersects the tangent from $M$ to the incircle (different from line $BC$) at a point $P$> Show that $AI$ is tangent to the circumcircle of triangle $MIP$.

Proposed by Tejaswi Navilarekallu
32 replies
Kayak
Jul 17, 2019
L13832
2 hours ago
D1015 : A strange EF for polynomials
Dattier   3
N 2 hours ago by Dattier
Source: les dattes à Dattier
Find all $P \in \mathbb R[x,y]$ with $P \not\in \mathbb R[x] \cup \mathbb R[y]$ and $\forall g,f$ homeomorphismes of $\mathbb R$, $P(f,g)$ is an homoemorphisme too.
3 replies
Dattier
Mar 16, 2025
Dattier
2 hours ago
Turkey EGMO TST 2017 P6
nimueh   4
N 2 hours ago by Nobitasolvesproblems1979
Source: Turkey EGMO TST 2017 P6
Find all pairs of prime numbers $(p,q)$, such that $\frac{(2p^2-1)^q+1}{p+q}$ and $\frac{(2q^2-1)^p+1}{p+q}$ are both integers.
4 replies
nimueh
Jun 1, 2017
Nobitasolvesproblems1979
2 hours ago
An inequality
JK1603JK   4
N 2 hours ago by Quantum-Phantom
Source: unknown
Let a,b,c>=0: ab+bc+ca=3 then maximize P=\frac{a^2b+b^2c+c^2a+9}{a+b+c}+\frac{abc}{2}.
4 replies
JK1603JK
Yesterday at 10:28 AM
Quantum-Phantom
2 hours ago
Inspired by Abelkonkurransen 2025
sqing   1
N 2 hours ago by kiyoras_2001
Source: Own
Let $ a,b,c $ be real numbers such that $  a^2+4b^2+16c^2= abc. $ Prove that $$\frac{1}{a}+\frac{1}{2b}+\frac{1}{4c}\geq -\frac{1}{16}$$Let $ a,b,c $ be real numbers such that $ 4a^2+9b^2+16c^2= abc. $ Prove that $$ \frac{1}{2a}+\frac{1}{3b}+\frac{1}{4c}\geq -\frac{1}{48}$$
1 reply
sqing
Yesterday at 1:06 PM
kiyoras_2001
2 hours ago
Geometry challenging question
srnjbr   0
3 hours ago
Given a triangle ABC. A1, B1 and C1 are the points of contact of the inner circumcircle of the triangle with the sides BC, AC and AB respectively. The point of contact of AA1 with B1C1 and the circumcircle are called L and Q respectively. M is the midpoint of B1C1. The point of intersection of lines BC and B1C1 is called T. P is the foot of the perpendicular drawn to AT from point L. Show that points A1, M, Q and P lie on a circle.
0 replies
srnjbr
3 hours ago
0 replies
Plane normal to vector
RenheMiResembleRice   0
3 hours ago
Source: Bian Wei
Solve the attached
0 replies
RenheMiResembleRice
3 hours ago
0 replies
Very easy inequality
pggp   2
N Wednesday at 6:06 PM by ali123456
Source: Polish Junior MO Second Round 2019
Let $x$, $y$ be real numbers, such that $x^2 + x \leq y$. Prove that $y^2 + y \geq x$.
2 replies
pggp
Oct 26, 2020
ali123456
Wednesday at 6:06 PM
Very easy inequality
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Source: Polish Junior MO Second Round 2019
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pggp
89 posts
#1
Y by
Let $x$, $y$ be real numbers, such that $x^2 + x \leq y$. Prove that $y^2 + y \geq x$.
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Faustus
1287 posts
#2 • 2 Y
Y by Mango247, pavel kozlov
$y^2+y\ge (x^2+x)^2+(x^2+x)= ((x^2+x)^2+x^2)+x\ge x$ since squares of reals are greater than zero.
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ali123456
44 posts
#3
Y by
Easy just notice that $y^2+y \ge y \ge x^2+x \ge x$ :cool:
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