Join our free webinar April 22 to learn about competitive programming!

G
Topic
First Poster
Last Poster
trolling geometry problem
iStud   1
N 40 minutes ago by iStud
Source: Monthly Contest KTOM April P3 Essay
Given a cyclic quadrilateral $ABCD$ with $BC<AD$ and $CD<AB$. Lines $BC$ and $AD$ intersect at $X$, and lines $CD$ and $AB$ intersect at $Y$. Let $E,F,G,H$ be the midpoints of sides $AB,BC,CD,DA$, respectively. Let $S$ and $T$ be points on segment $EG$ and $FH$, respectively, so that $XS$ is the angle bisector of $\angle{DXA}$ and $YT$ is the angle bisector of $\angle{DYA}$. Prove that $TS$ is parallel to $BD$ if and only if $AC$ divides $ABCD$ into two triangles with equal area.
1 reply
iStud
3 hours ago
iStud
40 minutes ago
Geometry Transformation Problems
ReticulatedPython   6
N Yesterday at 6:22 PM by ReticulatedPython
Problem 1:
A regular hexagon of side length $1$ is rotated $360$ degrees about one side. The space through which the hexagon travels during the rotation forms a solid. Find the volume of this solid.

Problem 2:

A regular octagon of side length $1$ is rotated $360$ degrees about one side. The space through which the octagon travels through during the rotation forms a solid. Find the volume of this solid.

Source:Own

Hint

Useful Formulas
6 replies
ReticulatedPython
Apr 17, 2025
ReticulatedPython
Yesterday at 6:22 PM
Camp Conway acceptance
fossasor   17
N Yesterday at 2:29 AM by fossasor
Hello! I've just been accepted into Camp Conway, but I'm not sure how popular this camp actually is, given that it's new. Has anyone else applied/has been accepted/is going? (I'm trying to figure out to what degree this acceptance was just lack of qualified applicants, so I can better predict my chances of getting into my preferred math camp.)
17 replies
fossasor
Feb 20, 2025
fossasor
Yesterday at 2:29 AM
Facts About 2025!
Existing_Human1   249
N Yesterday at 2:02 AM by EthanNg6
Hello AOPS,

As we enter the New Year, the most exciting part is figuring out the mathematical connections to the number we have now temporally entered

Here are some facts about 2025:
$$2025 = 45^2 = (20+25)(20+25)$$$$2025 = 1^3 + 2^3 +3^3 + 4^3 +5^3 +6^3 + 7^3 +8^3 +9^3 = (1+2+3+4+5+6+7+8+9)^2 = {10 \choose 2}^2$$
If anyone has any more facts about 2025, enlighted the world with a new appreciation for the year


(I got some of the facts from this video)
249 replies
Existing_Human1
Jan 1, 2025
EthanNg6
Yesterday at 2:02 AM
random problem i just thought about one day
ceilingfan404   5
N Yesterday at 1:47 AM by e_is_2.71828
i don't even know if this is solvable
Prove that there are finite/infinite powers of 2 where all the digits are also powers of 2. (For example, $4$ and $128$ are numbers that work, but $64$ and $1024$ don't work.)
5 replies
ceilingfan404
Sunday at 7:54 PM
e_is_2.71828
Yesterday at 1:47 AM
geometry problem
kjhgyuio   7
N Yesterday at 12:56 AM by Shan3t
........
7 replies
kjhgyuio
Sunday at 10:21 PM
Shan3t
Yesterday at 12:56 AM
2500th post
Solocraftsolo   31
N Sunday at 10:15 PM by Solocraftsolo
i keep forgetting to do these...


2500 is cool.

i am not very sentimental so im not going to post a math story or anything.

here are some problems though

p1p2p3

p4
31 replies
Solocraftsolo
Apr 16, 2025
Solocraftsolo
Sunday at 10:15 PM
2025 MATHCOUNTS State Hub
SirAppel   585
N Sunday at 9:27 PM by Eddie_tiger
Previous Years' "Hubs": (2022) (2023) (2024)Please Read

Now that it's April and we're allowed to discuss ...
[list=disc]
[*] CA: 43 (45 44 43 43 43 42 42 41 41 41)
[*] NJ: 43 (45 44 44 43 39 42 40 40 39 38) *
[*] NY: 42 (43 42 42 42 41 40)
[*] TX: 42 (43 43 43 42 42 40 40 38 38 38)
[*] MA: 41 (45 43 42 41)
[*] WA: 41 (41 45 42 41 41 41 41 41 41 40) *
[*]VA: 40 (41 40 40 40)
[*] FL: 39 (42 41 40 39 38 37 37)
[*] IN: 39 (41 40 40 39 36 35 35 35 34 34)
[*] NC: 39 (42 42 41 39)
[*] IL: 38 (41 40 39 38 38 38)
[*] OR: 38 (44 39 38 38)
[*] PA: 38 (41 40 40 38 38 37 36 36 34 34) *
[*] MD: 37 (43 39 39 37 37 37)
[*] AZ: 36 (40? 39? 39 36)
[*] CT: 36 (44 38 38 36 35 35 34 34 34 33 33)
[*] MI: 36 (39 41 41 36 37 37 36 36 36 36) *
[*] MN: 36 (40 36 36 36 35 35 35 34)
[*] CO: 35 (41 37 37 35 35 35 ?? 31 31 30) *
[*] GA: 35 (38 37 36 35 34 34 34 34 34 33)
[*] OH: 35 (41 37 36 35)
[*] AR: 34 (46 45 35 34 33 31 31 31 29 29)
[*] NV: 34 (41 38 ?? 34)
[*] TN: 34 (38 ?? ?? 34)
[*] WI: 34 (40 37 37 34 35 30 28 29 29 29) *
[*] HI: 32 (35 34 32 32)
[*] NH: 31 (42 35 33 31 30)
[*] DE: 30 (34 33 32 30 30 29 28 27 26? 24)
[*] SC: 30 (33 33 31 30)
[*] IA: 29 (33 30 31 29 29 29 29 29 29 29 29 29) *
[*] NE: 28 (34 30 28 28 27 27 26 26 25 25)
[*] SD: 22 (30 29 24 22 22 22 21 21 20 20)
[/list]
Cutoffs Unknown

* means that CDR is official in that state.

Notes

For those asking about the removal of the tiers, I'd like to quote Jason himself:
[quote=peace09]
learn from my mistakes
[/quote]

Help contribute by sharing your state's cutoffs!
585 replies
SirAppel
Apr 1, 2025
Eddie_tiger
Sunday at 9:27 PM
9 Did you get into Illinois middle school math Olympiad?
Gavin_Deng   2
N Sunday at 7:21 PM by Pi_isCool31415
I am simply curious of who got in.
2 replies
Gavin_Deng
Apr 19, 2025
Pi_isCool31415
Sunday at 7:21 PM
Weird Similarity
mithu542   3
N Sunday at 5:07 PM by zhoujef000
Is it just me or are the 2023 national sprint #21 and 2025 state target #4 strangely similar?
[quote=2023 Natioinal Sprint #21] A right triangle with integer side lengths has perimeter $N$ feet and area $N$ ft^2. What is the arithmetic mean of all possible values of $N$?[/quote]
[quote=2025 State Target #4]Suppose a right triangle has an area of 20 cm^2 and a perimeter of 40 cm. What is
the length of the hypotenuse, in centimeters?[/quote]
3 replies
mithu542
Apr 18, 2025
zhoujef000
Sunday at 5:07 PM
9 What is the most important topic in maths competition?
AVIKRIS   34
N Sunday at 3:46 PM by b2025tyx
I think arithmetic is the most the most important topic in math competitions.
34 replies
AVIKRIS
Apr 19, 2025
b2025tyx
Sunday at 3:46 PM
Sequence of projections is convergent
Filipjack   0
Apr 6, 2025
Source: Romanian National Olympiad 1997 - Grade 10 - Problem 3
A point $A_0$ and two lines $d_1$ and $d_2$ are given in the space. For each nonnegative integer $n$ we denote by $B_n$ the projection of $A_n$ on $d_2,$ and by $A_{n+1}$ the projection of $B_n$ on $d_1.$ Prove that there exist two segments $[A'A''] \subset d_1$ and $[B'B''] \subset d_2$ of length $0.001$ and a nonnegative integer $N$ such that $A_n \in [A'A'']$ and $B_n \in [B'B'']$ for any $n \ge N.$
0 replies
Filipjack
Apr 6, 2025
0 replies
Sequence of projections is convergent
G H J
G H BBookmark kLocked kLocked NReply
Source: Romanian National Olympiad 1997 - Grade 10 - Problem 3
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Filipjack
872 posts
#1
Y by
A point $A_0$ and two lines $d_1$ and $d_2$ are given in the space. For each nonnegative integer $n$ we denote by $B_n$ the projection of $A_n$ on $d_2,$ and by $A_{n+1}$ the projection of $B_n$ on $d_1.$ Prove that there exist two segments $[A'A''] \subset d_1$ and $[B'B''] \subset d_2$ of length $0.001$ and a nonnegative integer $N$ such that $A_n \in [A'A'']$ and $B_n \in [B'B'']$ for any $n \ge N.$
This post has been edited 1 time. Last edited by Filipjack, Apr 6, 2025, 4:56 PM
Z K Y
N Quick Reply
G
H
=
a