Stay ahead of learning milestones! Enroll in a class over the summer!

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k a April Highlights and 2025 AoPS Online Class Information
jlacosta   0
Apr 2, 2025
Spring is in full swing and summer is right around the corner, what are your plans? At AoPS Online our schedule has new classes starting now through July, so be sure to keep your skills sharp and be prepared for the Fall school year! Check out the schedule of upcoming classes below.

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[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
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0 replies
jlacosta
Apr 2, 2025
0 replies
Inequalities
sqing   25
N an hour ago by sqing
Let $   a,b    $ be reals such that $  a^2+ab+b^2 =3$ . Prove that
$$ \frac{4}{ 3}\geq \frac{1}{ a^2+5 }+ \frac{1}{ b^2+5 }+ab \geq -\frac{11}{4 }$$$$ \frac{13}{ 4}\geq \frac{1}{ a^2+5 }+ \frac{1}{ b^2+5 }+ab \geq -\frac{2}{3 }$$$$ \frac{3}{ 2}\geq  \frac{1}{ a^4+3 }+ \frac{1}{ b^4+3 }+ab \geq -\frac{17}{6 }$$$$ \frac{19}{ 6}\geq  \frac{1}{ a^4+3 }+ \frac{1}{ b^4+3 }-ab \geq -\frac{1}{2}$$Let $   a,b    $ be reals such that $  a^2-ab+b^2 =1 $ . Prove that
$$ \frac{3}{ 2}\geq \frac{1}{ a^2+3 }+ \frac{1}{ b^2+3 }+ab \geq \frac{4}{15 }$$$$ \frac{14}{ 15}\geq \frac{1}{ a^2+3 }+ \frac{1}{ b^2+3 }-ab \geq -\frac{1}{2 }$$$$ \frac{3}{ 2}\geq \frac{1}{ a^4+3 }+ \frac{1}{ b^4+3 }+ab \geq \frac{13}{42 }$$$$ \frac{41}{ 42}\geq \frac{1}{ a^4+3 }+ \frac{1}{ b^4+3 }-ab \geq -\frac{1}{2 }$$
25 replies
sqing
Apr 16, 2025
sqing
an hour ago
Three variables inequality
Headhunter   4
N 2 hours ago by lbh_qys
$\forall a\in R$ ,$~\forall b\in R$ ,$~\forall c \in R$
Prove that at least one of $(a-b)^{2}$, $(b-c)^{2}$, $(c-a)^{2}$ is not greater than $\frac{a^{2}+b^{2}+c^{2}}{2}$.

I assume that all are greater than it, but can't go more.
4 replies
Headhunter
Yesterday at 6:58 AM
lbh_qys
2 hours ago
Indonesia Regional MO 2019 Part A
parmenides51   23
N 3 hours ago by chinawgp
Indonesia Regional MO
Year 2019 Part A

Time: 90 minutes Rules


p1. In the bag there are $7$ red balls and $8$ white balls. Audi took two balls at once from inside the bag. The chance of taking two balls of the same color is ...


p2. Given a regular hexagon with a side length of $1$ unit. The area of the hexagon is ...


p3. It is known that $r, s$ and $1$ are the roots of the cubic equation $x^3 - 2x + c = 0$. The value of $(r-s)^2$ is ...


p4. The number of pairs of natural numbers $(m, n)$ so that $GCD(n,m) = 2$ and $LCM(m,n) = 1000$ is ...


p5. A data with four real numbers $2n-4$, $2n-6$, $n^2-8$, $3n^2-6$ has an average of $0$ and a median of $9/2$. The largest number of such data is ...


p6. Suppose $a, b, c, d$ are integers greater than $2019$ which are four consecutive quarters of an arithmetic row with $a <b <c <d$. If $a$ and $d$ are squares of two consecutive natural numbers, then the smallest value of $c-b$ is ...


p7. Given a triangle $ABC$, with $AB = 6$, $AC = 8$ and $BC = 10$. The points $D$ and $E$ lies on the line segment $BC$. with $BD = 2$ and $CE = 4$. The measure of the angle $\angle DAE$ is ...


p8. Sequqnce of real numbers $a_1,a_2,a_3,...$ meet $\frac{na_1+(n-1)a_2+...+2a_{n-1}+a_n}{n^2}=1$ for each natural number $n$. The value of $a_1a_2a_3...a_{2019}$ is ....


p9. The number of ways to select four numbers from $\{1,2,3, ..., 15\}$ provided that the difference of any two numbers at least $3$ is ...


p10. Pairs of natural numbers $(m , n)$ which satisfies $$m^2n+mn^2 +m^2+2mn = 2018m + 2019n + 2019$$are as many as ...


p11. Given a triangle $ABC$ with $\angle ABC =135^o$ and $BC> AB$. Point $D$ lies on the side $BC$ so that $AB=CD$. Suppose $F$ is a point on the side extension $AB$ so that $DF$ is perpendicular to $AB$. The point $E$ lies on the ray $DF$ such that $DE> DF$ and $\angle ACE = 45^o$. The large angle $\angle AEC$ is ...


p12. The set of $S$ consists of $n$ integers with the following properties: For every three different members of $S$ there are two of them whose sum is a member of $S$. The largest value of $n$ is ....


p13. The minimum value of $\frac{a^2+2b^2+\sqrt2}{\sqrt{ab}}$ with $a, b$ positive reals is ....


p14. The polynomial P satisfies the equation $P (x^2) = x^{2019} (x+ 1) P (x)$ with $P (1/2)= -1$ is ....


p15. Look at a chessboard measuring $19 \times 19$ square units. Two plots are said to be neighbors if they both have one side in common. Initially, there are a total of $k$ coins on the chessboard where each coin is only loaded exactly on one square and each square can contain coins or blanks. At each turn. You must select exactly one plot that holds the minimum number of coins in the number of neighbors of the plot and then you must give exactly one coin to each neighbor of the selected plot. The game ends if you are no longer able to select squares with the intended conditions. The smallest number of $k$ so that the game never ends for any initial square selection is ....
23 replies
parmenides51
Nov 11, 2021
chinawgp
3 hours ago
VOLUNTEERING OPPORTUNITIES OPEN TO HIGH/MIDDLE SCHOOLERS
im_space_cadet   13
N 4 hours ago by im_space_cadet
Hi everyone!
Do you specialize in contest math? Do you have a passion for teaching? Do you want to help leverage those college apps? Well, I have something for all of you.

I am im_space_cadet, and during the fall of last year, I opened my non-profit DeltaMathPrep which teaches students preparing for contest math the problem-solving skills they need in order to succeed at these competitions. Currently, we are very much understaffed and would greatly appreciate the help of more tutors on our platform.

Each week on Saturday and Wednesday, we meet once for each competition: Wednesday for AMC 8 and Saturday for AMC 10 and we go over a past year paper for the entire class. On both of these days, we meet at 9PM EST in the night.

This is a great opportunity for anyone who is looking to have a solid activity to add to their college resumes that requires low effort from tutors and is very flexible with regards to time.

This is the link to our non-profit for anyone who would like to view our initiative:
https://www.deltamathprep.org/

If you are interested in this opportunity, please send me a DM on AoPS or respond to this post expressing your interest. I look forward to having you all on the team!

Thanks,
im_space_cadet
13 replies
im_space_cadet
Yesterday at 2:27 PM
im_space_cadet
4 hours ago
Graph of polynomials
Ecrin_eren   1
N Yesterday at 5:36 PM by vanstraelen
The graph of the quadratic polynomial with real coefficients y = px^2 + qx + r, called G1, intersects the graph of the polynomial y = x^2, called G2, at points A and B. The lines tangent to G2 at points A and B intersect at point C. It is known that point C lies on G1. What is the value of p?
1 reply
Ecrin_eren
Yesterday at 3:00 PM
vanstraelen
Yesterday at 5:36 PM
polynomial with inequality
nhathhuyyp5c   1
N Apr 18, 2025 by matt_ve
Given the polynomial \( P(x) = x^3 + ax^2 + bx + c \), where \( a, b, c \) are real numbers. Suppose that \( P(x) \) has three distinct real roots and the polynomial \( Q(x) = P(x^2 + 12x - 32) \) has no real roots. Prove that
\[
P(1) > 69^3.
\]
1 reply
nhathhuyyp5c
Apr 18, 2025
matt_ve
Apr 18, 2025
Polynomials
CuriousBabu   12
N Apr 18, 2025 by wh0nix
\[ 
\frac{(x+y+z)^5 - x^5 - y^5 - z^5}{(x+y)(y+z)(z+x)} = 0 
\]
Find the number of real solutions.
12 replies
CuriousBabu
Apr 14, 2025
wh0nix
Apr 18, 2025
School Math Problem
math_cool123   6
N Apr 5, 2025 by anduran
Find all ordered pairs of nonzero integers $(a, b)$ that satisfy $$(a^2+b)(a+b^2)=(a-b)^3.$$
6 replies
math_cool123
Apr 2, 2025
anduran
Apr 5, 2025
Polynomial optimization problem
ReticulatedPython   2
N Apr 2, 2025 by Mathzeus1024
Let $$p(x)=-ax^4+x^3$$, where $a$ is a real number. Prove that for all positive $a$, $$p(x) \le \frac{27}{256a^3}.$$
2 replies
ReticulatedPython
Mar 31, 2025
Mathzeus1024
Apr 2, 2025
Prove that \( S \) contains all integers.
nhathhuyyp5c   1
N Mar 30, 2025 by GreenTea2593
Let \( S \) be a set of integers satisfying the following property: For every positive integer \( n \) and every set of coefficients \( a_0, a_1, \dots, a_n \in S \), all integer roots of the polynomial $P(x) = a_0 + a_1 x + \dots + a_n x^n
$ are also elements of \( S \). It is given that \( S \) contains all numbers of the form \( 2^a - 2^b \) where \( a, b \) are positive integers. Prove that \( S \) contains all integers.









1 reply
nhathhuyyp5c
Mar 29, 2025
GreenTea2593
Mar 30, 2025
Polynomial with roots in geometric progression
red_dog   0
Mar 21, 2025
Let $f\in\mathbb{C}[X], \ f=aX^3+bX^2+cX+d, \ a,b,c,d\in\mathbb{R}^*$ a polynomial whose roots $x_1,x_2,x_3$ are in geometric progression with ration $q\in(0,\infty)$. Find $S_n=x_1^n+x_2^n+x_3^n$.
0 replies
red_dog
Mar 21, 2025
0 replies
polynomial
nghik33ccb   3
N Mar 18, 2025 by nghik33ccb
Find all polynomials P(x) with coefficients 1 or -1 that satisfy P with all real roots
3 replies
nghik33ccb
Feb 11, 2025
nghik33ccb
Mar 18, 2025
2014 Community AIME / Marathon ... Algebra Medium #1 quartic
parmenides51   5
N Mar 16, 2025 by CubeAlgo15
Let there be a quartic function $f(x)$ with maximums $(4,5)$ and $(5,5)$. If $f(0) = -195$, and $f(10)$ can be expressed as $-n$ where $n$ is a positive integer, find $n$.

proposed by joshualee2000
5 replies
parmenides51
Jan 21, 2024
CubeAlgo15
Mar 16, 2025
function composition with quadratics yields no real roots (Auckland MO 2024 P11)
Equinox8   2
N Mar 12, 2025 by alexheinis
It is known that for quadratic polynomials $P(x)=x^2+ax+b$ and $Q(x)=x^2+cx+d$ the equation $P(Q(x))=Q(P(x))$ does not have real roots. Prove that $b \neq d$.
2 replies
Equinox8
Mar 12, 2025
alexheinis
Mar 12, 2025
computational with altitudes and midpoints (2009 HOMC Junior Q10)
parmenides51   2
N Jul 18, 2019 by amar_04
Let $ABC$ be an acute-angled triangle with $AB =4$ and $CD$ be the altitude through $C$ with $CD = 3$. Find the distance between the midpoints of $AD$ and $BC$
2 replies
parmenides51
Jul 18, 2019
amar_04
Jul 18, 2019
computational with altitudes and midpoints (2009 HOMC Junior Q10)
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parmenides51
30630 posts
#1 • 1 Y
Y by Adventure10
Let $ABC$ be an acute-angled triangle with $AB =4$ and $CD$ be the altitude through $C$ with $CD = 3$. Find the distance between the midpoints of $AD$ and $BC$
This post has been edited 1 time. Last edited by parmenides51, Jul 18, 2019, 2:17 PM
Reason: name typos
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Bashy99
698 posts
#2 • 2 Y
Y by Adventure10, Mango247
Solution.
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amar_04
1915 posts
#3 • 3 Y
Y by Path_to_Almighty, Adventure10, Mango247
Another Solution

This problem is similar to this https://artofproblemsolving.com/community/c6h56249_find_the_distance.
The OP's problem has a homothety with a scale factor of $\frac{1}{2}$ with the problem in the link. :D.
This post has been edited 11 times. Last edited by amar_04, Jul 18, 2019, 2:37 PM
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