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

G
Topic
First Poster
Last Poster
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.

Introductory: Grades 5-10

Prealgebra 1 Self-Paced

Prealgebra 1
Sunday, Apr 13 - Aug 10
Tuesday, May 13 - Aug 26
Thursday, May 29 - Sep 11
Sunday, Jun 15 - Oct 12
Monday, Jun 30 - Oct 20
Wednesday, Jul 16 - Oct 29

Prealgebra 2 Self-Paced

Prealgebra 2
Sunday, Apr 13 - Aug 10
Wednesday, May 7 - Aug 20
Monday, Jun 2 - Sep 22
Sunday, Jun 29 - Oct 26
Friday, Jul 25 - Nov 21

Introduction to Algebra A Self-Paced

Introduction to Algebra A
Monday, Apr 7 - Jul 28
Sunday, May 11 - Sep 14 (1:00 - 2:30 pm ET/10:00 - 11:30 am PT)
Wednesday, May 14 - Aug 27
Friday, May 30 - Sep 26
Monday, Jun 2 - Sep 22
Sunday, Jun 15 - Oct 12
Thursday, Jun 26 - Oct 9
Tuesday, Jul 15 - Oct 28

Introduction to Counting & Probability Self-Paced

Introduction to Counting & Probability
Wednesday, Apr 16 - Jul 2
Thursday, May 15 - Jul 31
Sunday, Jun 1 - Aug 24
Thursday, Jun 12 - Aug 28
Wednesday, Jul 9 - Sep 24
Sunday, Jul 27 - Oct 19

Introduction to Number Theory
Thursday, Apr 17 - Jul 3
Friday, May 9 - Aug 1
Wednesday, May 21 - Aug 6
Monday, Jun 9 - Aug 25
Sunday, Jun 15 - Sep 14
Tuesday, Jul 15 - Sep 30

Introduction to Algebra B Self-Paced

Introduction to Algebra B
Wednesday, Apr 16 - Jul 30
Tuesday, May 6 - Aug 19
Wednesday, Jun 4 - Sep 17
Sunday, Jun 22 - Oct 19
Friday, Jul 18 - Nov 14

Introduction to Geometry
Wednesday, Apr 23 - Oct 1
Sunday, May 11 - Nov 9
Tuesday, May 20 - Oct 28
Monday, Jun 16 - Dec 8
Friday, Jun 20 - Jan 9
Sunday, Jun 29 - Jan 11
Monday, Jul 14 - Jan 19

Intermediate: Grades 8-12

Intermediate Algebra
Monday, Apr 21 - Oct 13
Sunday, Jun 1 - Nov 23
Tuesday, Jun 10 - Nov 18
Wednesday, Jun 25 - Dec 10
Sunday, Jul 13 - Jan 18
Thursday, Jul 24 - Jan 22

Intermediate Counting & Probability
Wednesday, May 21 - Sep 17
Sunday, Jun 22 - Nov 2

Intermediate Number Theory
Friday, Apr 11 - Jun 27
Sunday, Jun 1 - Aug 24
Wednesday, Jun 18 - Sep 3

Precalculus
Wednesday, Apr 9 - Sep 3
Friday, May 16 - Oct 24
Sunday, Jun 1 - Nov 9
Monday, Jun 30 - Dec 8

Advanced: Grades 9-12

Olympiad Geometry
Tuesday, Jun 10 - Aug 26

Calculus
Tuesday, May 27 - Nov 11
Wednesday, Jun 25 - Dec 17

Group Theory
Thursday, Jun 12 - Sep 11

Contest Preparation: Grades 6-12

MATHCOUNTS/AMC 8 Basics
Wednesday, Apr 16 - Jul 2
Friday, May 23 - Aug 15
Monday, Jun 2 - Aug 18
Thursday, Jun 12 - Aug 28
Sunday, Jun 22 - Sep 21
Tues & Thurs, Jul 8 - Aug 14 (meets twice a week!)

MATHCOUNTS/AMC 8 Advanced
Friday, Apr 11 - Jun 27
Sunday, May 11 - Aug 10
Tuesday, May 27 - Aug 12
Wednesday, Jun 11 - Aug 27
Sunday, Jun 22 - Sep 21
Tues & Thurs, Jul 8 - Aug 14 (meets twice a week!)

AMC 10 Problem Series
Friday, May 9 - Aug 1
Sunday, Jun 1 - Aug 24
Thursday, Jun 12 - Aug 28
Tuesday, Jun 17 - Sep 2
Sunday, Jun 22 - Sep 21 (1:00 - 2:30 pm ET/10:00 - 11:30 am PT)
Monday, Jun 23 - Sep 15
Tues & Thurs, Jul 8 - Aug 14 (meets twice a week!)

AMC 10 Final Fives
Sunday, May 11 - Jun 8
Tuesday, May 27 - Jun 17
Monday, Jun 30 - Jul 21

AMC 12 Problem Series
Tuesday, May 27 - Aug 12
Thursday, Jun 12 - Aug 28
Sunday, Jun 22 - Sep 21
Wednesday, Aug 6 - Oct 22

AMC 12 Final Fives
Sunday, May 18 - Jun 15

F=ma Problem Series
Wednesday, Jun 11 - Aug 27

WOOT Programs
Visit the pages linked for full schedule details for each of these programs!


MathWOOT Level 1
MathWOOT Level 2
ChemWOOT
CodeWOOT
PhysicsWOOT

Programming

Introduction to Programming with Python
Thursday, May 22 - Aug 7
Sunday, Jun 15 - Sep 14 (1:00 - 2:30 pm ET/10:00 - 11:30 am PT)
Tuesday, Jun 17 - Sep 2
Monday, Jun 30 - Sep 22

Intermediate Programming with Python
Sunday, Jun 1 - Aug 24
Monday, Jun 30 - Sep 22

USACO Bronze Problem Series
Tuesday, May 13 - Jul 29
Sunday, Jun 22 - Sep 1

Physics

Introduction to Physics
Wednesday, May 21 - Aug 6
Sunday, Jun 15 - Sep 14
Monday, Jun 23 - Sep 15

Physics 1: Mechanics
Thursday, May 22 - Oct 30
Monday, Jun 23 - Dec 15

Relativity
Sat & Sun, Apr 26 - Apr 27 (4:00 - 7:00 pm ET/1:00 - 4:00pm PT)
Mon, Tue, Wed & Thurs, Jun 23 - Jun 26 (meets every day of the week!)
0 replies
jlacosta
Apr 2, 2025
0 replies
inquequality
ngocthi0101   10
N 14 minutes ago by MS_asdfgzxcvb
let $a,b,c > 0$ prove that
$\frac{a}{b} + \sqrt {\frac{b}{c}}  + \sqrt[3]{{\frac{c}{a}}} > \frac{5}{2}$
10 replies
ngocthi0101
Sep 26, 2014
MS_asdfgzxcvb
14 minutes ago
Functional Equation
AnhQuang_67   5
N 18 minutes ago by jasperE3
Find all functions $f: \mathbb{R} \to \mathbb{R}$ satisfying $$2\cdot f\Big(\dfrac{-xy}{2}+f(x+y)\Big)=xf(y)+yf(x), \forall x, y \in \mathbb{R} $$
5 replies
AnhQuang_67
Yesterday at 4:50 PM
jasperE3
18 minutes ago
Special line through antipodal
Phorphyrion   8
N 21 minutes ago by optimusprime154
Source: 2025 Israel TST Test 1 P2
Triangle $\triangle ABC$ is inscribed in circle $\Omega$. Let $I$ denote its incenter and $I_A$ its $A$-excenter. Let $N$ denote the midpoint of arc $BAC$. Line $NI_A$ meets $\Omega$ a second time at $T$. The perpendicular to $AI$ at $I$ meets sides $AC$ and $AB$ at $E$ and $F$ respectively. The circumcircle of $\triangle BFT$ meets $BI_A$ a second time at $P$, and the circumcircle of $\triangle CET$ meets $CI_A$ a second time at $Q$. Prove that $PQ$ passes through the antipodal to $A$ on $\Omega$.
8 replies
Phorphyrion
Oct 28, 2024
optimusprime154
21 minutes ago
PoP+Parallel
Solilin   1
N an hour ago by sansgankrsngupta
Source: Titu Andreescu, Lemmas in Olympiad Geometry
Let ABC be a triangle and let D, E, F be the feet of the altitudes, with D on BC, E on CA, and F on AB. Let the parallel through D to EF meet AB at X and AC at Y. Let T be the intersection of EF with BC and let M be the midpoint of side BC. Prove that the points T, M, X, Y are concyclic.
1 reply
Solilin
an hour ago
sansgankrsngupta
an hour ago
School Math Problem
math_cool123   6
N 5 hours ago 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
5 hours ago
New geometry problem
titaniumfalcon   3
N Yesterday at 11:16 PM by mathprodigy2011
Post any solutions you have, with explanation or proof if possible, good luck!
3 replies
titaniumfalcon
Thursday at 10:40 PM
mathprodigy2011
Yesterday at 11:16 PM
Geo Mock #10
Bluesoul   2
N Yesterday at 8:26 PM by Bluesoul
Consider acute $\triangle{ABC}$ with $AB=10$, $AC<BC$ and area $135$. The circle $\omega$ with diameter $AB$ meets $BC$ at $E$. Let the orthocenter of the triangle be $H$, connect $CH$ and extend to meet $\omega$ at $N$ such that $NC>HC$ and $NE$ is the diameter of $\omega$. Draw the circumcircle $\Gamma$ of $\triangle{AHB}$, chord $XY$ of $\Gamma$ is tangent to $\omega$ and it passes through $N$, compute $XY$.
2 replies
Bluesoul
Apr 1, 2025
Bluesoul
Yesterday at 8:26 PM
Inequalities
sqing   4
N Yesterday at 3:28 PM by sqing
Let $ a, b,c\geq 0 $ and $ 2a+3b+ 4c=11.$ Prove that
$$a+ab+abc\leq\frac{49}{6}$$Let $ a, b,c\geq 0 $ and $ 2a+3b+ 4c=10.$ Prove that
$$a+ab+abc\leq\frac{169}{24}$$Let $ a, b,c\geq 0 $ and $ 2a+3b+ 4c=14.$ Prove that
$$a+ab+abc\leq\frac{63+5\sqrt 5}{6}$$Let $ a, b,c\geq 0 $ and $ 2a+3b+ 4c=32.$ Prove that
$$a+ab+abc\leq48+\frac{64\sqrt{2}}{3}$$
4 replies
sqing
Apr 1, 2025
sqing
Yesterday at 3:28 PM
Geo Mock #9
Bluesoul   1
N Yesterday at 3:19 PM by vanstraelen
Consider $\triangle{ABC}$ with $AB=12, AC=22$. The points $D,E$ lie on $AB,AC$ respectively, such that $\frac{AD}{BD}=\frac{AE}{CE}=3$. Extend $CD,BE$ to meet the circumcircle of $\triangle{ABC}$ at $P,Q$ respectively. Let the circumcircles of $\triangle{ADP}, \triangle{AEQ}$ meet at points $A,T$. Extend $AT$ to $BC$ at $R$, given $AR=16$, find $[ABC]$.
1 reply
Bluesoul
Apr 1, 2025
vanstraelen
Yesterday at 3:19 PM
Geo Mock #6
Bluesoul   1
N Yesterday at 1:59 PM by vanstraelen
Consider triangle $ABC$ with $AB=5, BC=8, AC=7$, denote the incenter of the triangle as $I$. Extend $BI$ to meet the circumcircle of $\triangle{AIC}$ at $Q\neq I$, find the length of $QC$.
1 reply
Bluesoul
Apr 1, 2025
vanstraelen
Yesterday at 1:59 PM
Congruence
Ecrin_eren   1
N Yesterday at 1:39 PM by Ecrin_eren
Find the number of integer pairs (x, y) satisfying the congruence equation:

3y² + 3x²y + y³ ≡ 3x² (mod 41)

for 0 ≤ x, y < 41.

1 reply
Ecrin_eren
Thursday at 10:34 AM
Ecrin_eren
Yesterday at 1:39 PM
Probability
Ecrin_eren   1
N Yesterday at 1:38 PM by Ecrin_eren
In a board, James randomly writes A , B or C in each cell. What is the probability that, for every row and every column, the number of A 's modulo 3 is equal to the number of B's modulo 3?

1 reply
Ecrin_eren
Thursday at 11:21 AM
Ecrin_eren
Yesterday at 1:38 PM
Excalibur Identity
jjsunpu   9
N Yesterday at 12:21 PM by fruitmonster97
proof is below
9 replies
jjsunpu
Thursday at 3:27 PM
fruitmonster97
Yesterday at 12:21 PM
.problem.
Cobedangiu   2
N Yesterday at 12:06 PM by Lankou
Find the integer coefficients after expanding Newton's binomial:
$$(\frac{3}{2}-\frac{2}{3}x^2)^n (n \in Z)$$
2 replies
Cobedangiu
Yesterday at 6:20 AM
Lankou
Yesterday at 12:06 PM
Point of concurrence on the altitude
fprosk   12
N Jan 10, 2016 by 28121941
Source: Iberoamerican 2015 #4
Let $ABC$ be an acute triangle and let $D$ be the foot of the perpendicular from $A$ to side $BC$. Let $P$ be a point on segment $AD$. Lines $BP$ and $CP$ intersect sides $AC$ and $AB$ at $E$ and $F$, respectively. Let $J$ and $K$ be the feet of the peroendiculars from $E$ and $F$ to $AD$, respectively. Show that

$\frac{FK}{KD}=\frac{EJ}{JD}$.
12 replies
fprosk
Nov 11, 2015
28121941
Jan 10, 2016
Point of concurrence on the altitude
G H J
G H BBookmark kLocked kLocked NReply
Source: Iberoamerican 2015 #4
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
fprosk
681 posts
#1 • 2 Y
Y by Adventure10, Mango247
Let $ABC$ be an acute triangle and let $D$ be the foot of the perpendicular from $A$ to side $BC$. Let $P$ be a point on segment $AD$. Lines $BP$ and $CP$ intersect sides $AC$ and $AB$ at $E$ and $F$, respectively. Let $J$ and $K$ be the feet of the peroendiculars from $E$ and $F$ to $AD$, respectively. Show that

$\frac{FK}{KD}=\frac{EJ}{JD}$.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Math_tricks
32 posts
#2 • 2 Y
Y by Adventure10, Mango247
Suppose that angle FDA=x and angle EDA=y.By Ceva, we get BF/AF*AE/CE*CD/BD=1. After using law of sines in triangles AFD and AED we get that sin(y)/sin(x)*cos(x)/cos(y)*cos(C-y)/cos(y-C)*cos(x-B)/cos(B-x)=1. We have cos(y-C)=cos(C-y) and cos(x-B)=cos(B-x). So, sin(y)/sin(x)*cos(x)/cos(y)=1. This gives us x=y and tan(x)=tan(y) which is echivalent to FK/KD=EJ/JD
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
aleph_zero
18 posts
#3 • 2 Y
Y by UI_MathZ_25, Adventure10
Solution without trig
1. $\triangle FKP\sim \triangle CDP$ - $\frac{KF}{KP}=\frac{KF+CD}{KD}$. So $\frac{KF}{KD}=\frac{KF}{KP}-\frac{CD}{KD}=\frac{CD}{DP}-\frac{CD}{KD}=\frac{CD\cdot KP}{KD\cdot DP}$.
2. $\triangle EJP\sim\triangle BDP$ - $\frac{EJ}{JP}=\frac{EJ+BD}{ED}$. So $\frac{EJ}{ED}=\frac{EJ}{JP}-\frac{BD}{ED}=\frac{BD\cdot JP}{JD\cdot DP}$.
Therefore $\frac{KF}{KP}=\frac{EJ}{JP}$ is equivalent to
$\frac{BD\cdot JP}{JD}=\frac{CD\cdot KP}{KD}$
or
$\frac{BD}{CD}=\frac{KP}{KD}\cdot \frac{JD}{JP}$
By Ceva and obvious similarities we have
$1=\frac{BD}{CD}\cdot\frac{CE}{AE}\cdot\frac{AF}{BF}=\frac{BD}{CD}\cdot\frac{JD}{AJ}\cdot\frac{AK}{KD}$.
Therefore
$\frac{AJ}{AK}\cdot\frac{KD}{JD}=\frac{BD}{CD}=\frac{KP}{KD}\cdot\frac{JD}{JP}$
which is equivalent to
$\frac{AJ\cdot JP}{JD^2}=\frac{AK\cdot KP}{KD^2}$.
But
$\frac{AK\cdot KP}{KD^2}=\frac{AF}{FB}\cdot\frac{KP}{KP+CD}=\frac{AF}{FB}\cdot\frac{FP}{CF}$.
and
$\frac{AJ\cdot JP}{JD^2}=\frac{AE}{EC}\cdot\frac{EP}{KP+BD}=\frac{AE}{EC}\cdot\frac{EP}{EB}$.
And finally, using van Aubel's theorem and Ceva
$\frac{FB}{AF}\cdot\frac{FP+CP}{FP}=\frac{FB}{AF}\cdot\left(1+\frac{CD}{DB}+\frac{CE}{EA}\right)=\frac{FB}{AF}+\frac{CE}{EA}+\frac{FB}{AF}\cdot\frac{CE}{EA}$,
$\frac{EC}{EA}\cdot\frac{EP+PB}{EP}=\frac{EC}{EA}\left(1+\frac{FB}{AF}+\frac{BD}{CD}\right)=\frac{CE}{EA}+\frac{FB}{AF}+\frac{CE}{EA}\cdot\frac{FB}{AF}$.
Hence $\frac{AK\cdot KP}{KD^2}=\frac{AJ\cdot JP}{JD^2}\Leftrightarrow \frac{FK}{KD}=\frac{EJ}{JD}$.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Dukejukem
695 posts
#4 • 3 Y
Y by Ricochet, Adventure10, Mango247
Denote $X \equiv EF \cap AD, Y \equiv EF \cap BC.$ Since the cevians $AD, BE, CF$ are concurrent in $\triangle ABC$, we have $-1 = A(B, C; D, Y) = (F, E; X, Y).$ But since $DX \perp DY$, it is well-known (Lemma 5) that $DX$ bisects $\angle EDF.$ Hence, $\angle EDJ = \angle FDK \implies \triangle EDJ \sim \triangle FDK$, and the desired result follows.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Math_CYCR
431 posts
#5 • 3 Y
Y by alexgsi, Adventure10, Mango247
Another trig solution :-D

First denote:

$\angle FDB= \alpha$
$\angle ADF= \beta$
$\angle EDA= \omega$
$\angle CDE= \phi$

By the generalized angle bisector theorem in $\triangle ADB \longrightarrow \frac{\sin \alpha }{\sin \beta } = \frac{BF*DA}{FA*BD}$

By the generalized angle bisector theorem in $\triangle ADB \longrightarrow \frac{\sin \omega }{\sin \phi } = \frac{AE*DC}{EC*AD}$

Apply Ceva and we get:

$\frac{\sin \alpha }{\sin \beta} *  \frac{\sin \omega }{\sin \phi } = \frac{AE*DC}{EC} * \frac{BF}{FA*BD} = 1$

$\frac{\sin \alpha }{\sin \beta} =  \frac{\sin \phi }{\sin \omega }$

Lemma.- Let $a+b=x+y<180$ and $ \frac{\sin a}{\sin b} = \frac{\sin x}{\sin y} \longrightarrow a=x, b=y$ this can be easily done applying the generalized angle bisector theorem in an isosceles triangle.

In this case $\alpha + \beta = \phi + \omega=90$
So, we get $\alpha = \phi$ and $\beta = \omega$ which implies also using the fact that $\angle EJD = \angle  FKD=90$ that $\triangle FKD \sim \triangle EJD$ and the desired result follows ;)
This post has been edited 1 time. Last edited by Math_CYCR, Nov 11, 2015, 11:34 PM
Reason: Text
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
drmzjoseph
445 posts
#6 • 2 Y
Y by Adventure10, Mango247
Consider the homology $f: P \rightarrow P'$ that send $BC$ to the infinity, is clear $A'E'P'F'$ is a parallelogram, also $J'E' \parallel F'K' \parallel BC$, so $F'J'E'K'$ is a parallelogram($F'J' \parallel K'E'$) this implies $FJ,KE$ and $BC$ are concurrent (point $X$)
\[\Rightarrow \frac{XJ}{XF}=\frac{JD}{KD}=\frac{EJ}{FK}\]
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
drmzjoseph
445 posts
#7 • 1 Y
Y by Adventure10
According to my proof we can put an easy generalization

Let $ABC$ be a triangle, and the cevians $AE,BD$ and $CF$ concurrent at $P$, the parallel lines to $BC$ from $E$ and $F$ cut to $AD$ at $J$ and $K$ respectively. Prove that \[\frac{FK}{KD}=\frac{EJ}{JD}\]
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
armann
18 posts
#9 • 3 Y
Y by Adventure10, Mango247, AlexCenteno2007
fprosk wrote:
Let $ABC$ be an acute triangle and let $D$ be the foot of the perpendicular from $A$ to side $BC$. Let $P$ be a point on segment $AD$. Lines $BP$ and $CP$ intersect sides $AC$ and $AB$ at $E$ and $F$, respectively. Let $J$ and $K$ be the feet of the peroendiculars from $E$ and $F$ to $AD$, respectively. Show that

$\frac{FK}{KD}=\frac{EJ}{JD}$.

Its very easy with blanchet theorem.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
jayme
9775 posts
#10 • 2 Y
Y by Adventure10, Mango247
Dear mathlinkers,

see also
http://www.artofproblemsolving.com/community/c6t48f6h1162621_iberoamerican_olympiad_2015_problem_4

Sincerely
Jean-Louis
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
fprosk
681 posts
#11 • 2 Y
Y by Adventure10, Mango247
This problem actually comes out rather nicely analytically. Let D be the origin, A be on the y axis, P on the y axis between D and A, and B and C on opposite sides of D on the x axis. Then you get some simple equations for the lines AB, AC, CP, and BP, which you can use to find the coordinates of E and F. FK and KD are the distances from F to the y and x axes respectively while EJ and JD are the distances from E to the y and x axes respectively, and you can see that the ratios are the same.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
drmzjoseph
445 posts
#12 • 2 Y
Y by FabrizioFelen, Adventure10
I have a doubt
Why to select a geometry easy problem (trivial) in Iberoamerican olympiad? in recent years.

This problem I solved with projective geometry, although is trivial by Blanchet's Theorem, do to think like a region with a bad geometry

I accept all kinds of criticism, is only a doubt. Sorry my english isn't good
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
jbaca
225 posts
#13 • 3 Y
Y by drmzjoseph, Adventure10, Mango247
I agree with you. Geometry problems in the OIMs 2013, 2014, 2015 have been quite easy. I really miss a geometry problem as problem 3 or 6 in the contest. Moreover, this problem is a direct application of a very well-known theorem and an approach using projective geometry (as we can see in the previous posts) is possible. I hope that in the next OIM appear a difficult geometry problem, as in 2010 and 2011.
This post has been edited 1 time. Last edited by jbaca, Dec 10, 2015, 6:12 PM
Reason: A missing parentheses.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
28121941
152 posts
#14 • 2 Y
Y by drmzjoseph, Adventure10
Yes you are right. It seems that the International Jury do not want choose hard geometry problems, and the results in 2014 and 2015 was that the gold medals were awarded to the students who have 42 points.
Get 41 points in an International competition and do not get god medal is, I think, very frustrating.
Z K Y
N Quick Reply
G
H
=
a