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.

WOOT early bird pricing is in effect, don’t miss out! If you took MathWOOT Level 2 last year, no worries, it is all new problems this year! Our Worldwide Online Olympiad Training program is for high school level competitors. AoPS designed these courses to help our top students get the deep focus they need to succeed in their specific competition goals. Check out the details at this link for all our WOOT programs in math, computer science, chemistry, and physics.

Looking for summer camps in math and language arts? Be sure to check out the video-based summer camps offered at the Virtual Campus that are 2- to 4-weeks in duration. There are middle and high school competition math camps as well as Math Beasts camps that review key topics coupled with fun explorations covering areas such as graph theory (Math Beasts Camp 6), cryptography (Math Beasts Camp 7-8), and topology (Math Beasts Camp 8-9)!

Be sure to mark your calendars for the following events:
[list][*]April 3rd (Webinar), 4pm PT/7:00pm ET, Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor
[*]April 8th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MATHCOUNTS State Discussion
April 9th (Webinar), 4:00pm PT/7:00pm ET, Learn about Video-based Summer Camps at the Virtual Campus
[*]April 10th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MathILy and MathILy-Er Math Jam: Multibackwards Numbers
[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
Our full course list for upcoming classes is below:
All classes run 7:30pm-8:45pm ET/4:30pm - 5:45pm PT unless otherwise noted.

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0 replies
jlacosta
Apr 2, 2025
0 replies
Weird Inequality Problem
Omerking   1
N 6 minutes ago by Nuran2010
Following inequality is given:
$$3\geq ab+bc+ca\geq \dfrac{1}{3}$$Find the range of values that can be taken by :
$1)a+b+c$
$2)abc$

Where $a,b,c$ are positive reals.
1 reply
Omerking
27 minutes ago
Nuran2010
6 minutes ago
Weakly-periodic functions compared with lines
Miquel-point   2
N 8 minutes ago by dgrozev
Source: KoMaL A. 895
Let's call a function $f:\mathbb R\to\mathbb R$ weakly periodic if it is continuous and $f(x+1)=f(f(x))+1$ for all $x\in\mathbb R$.
a) Does there exist a weakly periodic function such that $f(x)>x$ for all $x\in\mathbb R$?
b) Does there exist a weakly periodic function such that $f(x)<x$ for all $x\in\mathbb R$?

Proposed by: András Imolay, Budapest
2 replies
Miquel-point
Jan 13, 2025
dgrozev
8 minutes ago
Beatty sequences of continued fractions
Miquel-point   1
N 31 minutes ago by starchan
Source: KoMaL A. 903
Let the irrational number
\[\alpha =1-\cfrac{1}{2a_1-\cfrac{1}{2a_2-\cfrac{1}{2a_3-\cdots}}}\]where coefficients $a_1, a_2, \ldots$ are positive integers, infinitely many of which are greater than $1$. Prove that for every positive integer $N$ at least half of the numbers $\lfloor \alpha\rfloor, \lfloor 2\alpha\rfloor, \ldots, \lfloor N\alpha\rfloor$ are even.

Proposed by Géza Kós, Budapest
1 reply
Miquel-point
Yesterday at 5:41 PM
starchan
31 minutes ago
Easy Inceter related geometry
Pluto1708   10
N 36 minutes ago by ihategeo_1969
Source: STEMS 2021/CAT B/P3
Let $ABC$ be a triangle with $I$ as incenter.The incircle touches $BC$ at $D$.Let $D'$ be the antipode of $D$ on the incircle.Make a tangent at $D'$ to incircle.Let it meet $(ABC)$ at $X,Y$ respectively.Let the other tangent from $X$ meet the other tangent from $Y$ at $Z$.Prove that $(ZBD)$ meets $IB$ at the midpoint of $IB$
10 replies
Pluto1708
Jan 24, 2021
ihategeo_1969
36 minutes ago
No more topics!
Three Thales circles
randomusername   0
Jul 16, 2014
Source: Kürschák 1995, problem 3
Points $A$, $B$, $C$, $D$ are such that no three of them are collinear. Let $E=AB\cap CD$ and $F=BC\cap DA$. Let $k_1$, $k_2$ and $k_3$ denote the circles with diameter $\overline{AC}$, $\overline{BD}$ and $\overline{EF}$, respectively. Prove that either $k_1,k_2,k_3$ pass through one point, or no two of them intersect.
0 replies
randomusername
Jul 16, 2014
0 replies
Three Thales circles
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Source: Kürschák 1995, problem 3
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randomusername
1059 posts
#1 • 2 Y
Y by Adventure10, Mango247
Points $A$, $B$, $C$, $D$ are such that no three of them are collinear. Let $E=AB\cap CD$ and $F=BC\cap DA$. Let $k_1$, $k_2$ and $k_3$ denote the circles with diameter $\overline{AC}$, $\overline{BD}$ and $\overline{EF}$, respectively. Prove that either $k_1,k_2,k_3$ pass through one point, or no two of them intersect.
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