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
all functions satisfying f(x+yf(x))+y = xy + f(x+y)
falantrng   4
N a few seconds ago by Sadigly
Source: Balkan MO 2025 P3
Find all functions $f\colon \mathbb{R} \rightarrow \mathbb{R}$ such that for all $x,y \in \mathbb{R}$,
\[f(x+yf(x))+y = xy + f(x+y).\]
Proposed by Giannis Galamatis, Greece
4 replies
+11 w
falantrng
19 minutes ago
Sadigly
a few seconds ago
functional inequality f(x)^2>= max{f(y)^2, (y-x)f(y)} for 0<=x<y
tom-nowy   1
N 2 minutes ago by tom-nowy
Source: presented in a PDE textbook.
Let $f : [0, \infty) \to [0, \infty)$ be a function such that for any real numbers $x,y$ satisfying $0 \le x < y$,
$$ f(x)^2 \geq \max \left\{ f(y)^2, \; (y-x)f(y) \right\} .$$Given $f(0)=1$, find the value of $f(5)$.
1 reply
tom-nowy
May 27, 2013
tom-nowy
2 minutes ago
Polygons Which Don't Fit
somebodyyouusedtoknow   1
N 2 minutes ago by kiyoras_2001
Source: San Diego Honors Math Contest 2025 Part II, Problem 1
Let $P_1,P_2,\ldots,P_n$ be polygons, no two of which are similar. Show that there are polygons $Q_1,Q_2,\ldots,Q_n$ where $Q_i$ is similar to $P_i$ so that for no $i \neq j$ does $Q_i$ contain a polygon that's congruent to $Q_j$.

Note. Here, the word "contain" means for the construction we have, we cannot select a size for $Q_j$ so that $Q_j$ is wholly contained in $Q_i$, and so it does not intersect the edges of $Q_i$ at all.
1 reply
+1 w
somebodyyouusedtoknow
Yesterday at 11:28 PM
kiyoras_2001
2 minutes ago
Range of argument of iw+3i-4w
Kunihiko_Chikaya   1
N 4 minutes ago by Mathzeus1024
Source: 1999 Waseda University entrance exam/Science and Engineering
Answer the following questions.

(i) When a complex number $z$ satisfies $|z-1|=1$, draw the locus of the points $w$ determined by $w=\frac{z-i}{z+i}$ in the complex plane.

(ii) For $w$ in (i), find the range of argument $\theta \ (0\leqq \theta<2\pi)$ of $iw+3i-4$.
1 reply
Kunihiko_Chikaya
Aug 4, 2014
Mathzeus1024
4 minutes ago
No more topics!
diagonal intersection of cyclic ABCD is incenter of BMC, circumcircles related
parmenides51   1
N Sep 28, 2019 by MathMonster0923
Source: 2013 Oral Moscow Geometry Olympiad grades 10-11 p1
Diagonals of a cyclic quadrilateral $ABCD$ intersect at point $O$. The circumscribed circles of triangles $AOB$ and $COD$ intersect at point $M$ on the side $AD$. Prove that the point $O$ is the center of the inscribed circle of the triangle $BMC$.
1 reply
parmenides51
Aug 16, 2019
MathMonster0923
Sep 28, 2019
diagonal intersection of cyclic ABCD is incenter of BMC, circumcircles related
G H J
Source: 2013 Oral Moscow Geometry Olympiad grades 10-11 p1
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parmenides51
30649 posts
#1 • 1 Y
Y by Adventure10
Diagonals of a cyclic quadrilateral $ABCD$ intersect at point $O$. The circumscribed circles of triangles $AOB$ and $COD$ intersect at point $M$ on the side $AD$. Prove that the point $O$ is the center of the inscribed circle of the triangle $BMC$.
This post has been edited 2 times. Last edited by parmenides51, Feb 25, 2024, 7:28 AM
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MathMonster0923
36 posts
#2 • 2 Y
Y by Adventure10, Mango247
$\angle CMO = \angle CDO = \angle CDB = \angle CAB = \angle OAB = \angle OMB$
$\angle MBO = \angle MAO = \angle DAC = \angle DBC = \angle OBC$
$O$ is incenter of $BMC$
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