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

G
Topic
First Poster
Last Poster
k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
Yesterday at 11:16 PM
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

Are you interested in working towards MATHCOUNTS and don’t know where to start? We have you covered! If you have taken Prealgebra, then you are ready for MATHCOUNTS/AMC 8 Basics. Already aiming for State or National MATHCOUNTS and harder AMC 8 problems? Then our MATHCOUNTS/AMC 8 Advanced course is for you.

Summer camps are starting next month at the Virtual Campus in math and language arts that are 2 - to 4 - weeks in duration. Spaces are still available - don’t miss your chance to have an enriching summer experience. 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 upcoming events:
[list][*]May 9th, 4:30pm PT/7:30pm ET, Casework 2: Overwhelming Evidence — A Text Adventure, a game where participants will work together to navigate the map, solve puzzles, and win! All are welcome.
[*]May 19th, 4:30pm PT/7:30pm ET, What's Next After Beast Academy?, designed for students finishing Beast Academy and ready for Prealgebra 1.
[*]May 20th, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 1 Math Jam, Problems 1 to 4, join the Canada/USA Mathcamp staff for this exciting Math Jam, where they discuss solutions to Problems 1 to 4 of the 2025 Mathcamp Qualifying Quiz!
[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/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
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
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
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
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
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
Tuesday, May 6 - Aug 19
Wednesday, Jun 4 - Sep 17
Sunday, Jun 22 - Oct 19
Friday, Jul 18 - Nov 14

Introduction to Geometry
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

Paradoxes and Infinity
Mon, Tue, Wed, & Thurs, Jul 14 - Jul 16 (meets every day of the week!)

Intermediate: Grades 8-12

Intermediate Algebra
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
Sunday, Jun 1 - Aug 24
Wednesday, Jun 18 - Sep 3

Precalculus
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
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
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

AIME Problem Series A
Thursday, May 22 - Jul 31

AIME Problem Series B
Sunday, Jun 22 - Sep 21

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
Mon, Tue, Wed & Thurs, Jun 23 - Jun 26 (meets every day of the week!)
0 replies
jlacosta
Yesterday at 11:16 PM
0 replies
P(x), integer, integer roots, P(0) =-1,P(3) = 128
parmenides51   3
N 2 minutes ago by Rohit-2006
Source: Nordic Mathematical Contest 1989 #1
Find a polynomial $P$ of lowest possible degree such that
(a) $P$ has integer coefficients,
(b) all roots of $P$ are integers,
(c) $P(0) = -1$,
(d) $P(3) = 128$.
3 replies
parmenides51
Oct 5, 2017
Rohit-2006
2 minutes ago
2017 CGMO P1
smy2012   9
N 6 minutes ago by Bardia7003
Source: 2017 CGMO P1
(1) Find all positive integer $n$ such that for any odd integer $a$, we have $4\mid a^n-1$
(2) Find all positive integer $n$ such that for any odd integer $a$, we have $2^{2017}\mid a^n-1$
9 replies
smy2012
Aug 13, 2017
Bardia7003
6 minutes ago
Euler's function
luutrongphuc   1
N 21 minutes ago by luutrongphuc
Find all real numbers \(\alpha\) such that for every positive real \(c\), there exists an integer \(n>1\) satisfying
\[
\frac{\varphi(n!)}{n^\alpha\,(n-1)!} \;>\; c.
\]
1 reply
luutrongphuc
an hour ago
luutrongphuc
21 minutes ago
Square problem
Jackson0423   1
N 36 minutes ago by maromex
Construct a square such that the distances from an interior point to the vertices (in clockwise order) are
1,2,3,4, respectively.
1 reply
Jackson0423
an hour ago
maromex
36 minutes ago
No more topics!
Find relation in triangle
Rushil   19
N Aug 6, 2023 by Krishijivi
Source: INMO 1992 Problem 1
In a triangle $ABC$, $\angle A = 2 \cdot \angle B$. Prove that $a^2 = b (b+c)$.
19 replies
Rushil
Oct 3, 2005
Krishijivi
Aug 6, 2023
Find relation in triangle
G H J
Source: INMO 1992 Problem 1
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Rushil
1592 posts
#1 • 2 Y
Y by Adventure10, Mango247
In a triangle $ABC$, $\angle A = 2 \cdot \angle B$. Prove that $a^2 = b (b+c)$.
This post has been edited 1 time. Last edited by Rushil, Oct 4, 2005, 5:39 AM
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
shobber
3498 posts
#2 • 2 Y
Y by Adventure10, Mango247
Rushil wrote:
INMO 1992 Problem 1

In a triangle $ABC$ , $\angle A = 2 \times \angle B$. Prove that $a^2 = b (b+c)$
Try to search for Double Angle Theorem.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Andreas
578 posts
#3 • 3 Y
Y by AmitayasB, Adventure10, Mango247
$\frac{a}{\sin 2x} = \frac{b}{\sin x} = \frac{c}{\sin 3x}$ $\Longrightarrow$ $c = b(4\cos^2 x - 1)$ and $a = 2b\cos x$.
$b(b + c) = 4b^2\cos^2 x = a^2$
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Ezbakhe Yassin
146 posts
#4 • 1 Y
Y by Adventure10
Andreas wrote:
$\frac{a}{\sin 2x} = \frac{b}{\sin x} = \frac{c}{\sin 3x}$

How did you get this one?
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
mathmanman
1444 posts
#5 • 1 Y
Y by Adventure10
That's just the law of sines ;)
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Elemennop
1421 posts
#6 • 1 Y
Y by Adventure10
$\sin{C}=\sin{(180-A-B)}=\sin{(180-3x)}=\sin{(3x)}$, Because $\sin{x}=\sin{(180-x)}$.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
The QuattoMaster 6000
1184 posts
#7 • 1 Y
Y by Adventure10
Rushil wrote:
In a triangle $ ABC$, $ \angle A = 2 \cdot \angle B$. Prove that $ a^2 = b (b + c)$.
Sorry for awakening an old topic, but here's a neat solution that no-one here mentioned already:
Solution
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
earth
99 posts
#8 • 3 Y
Y by Samujjal101, Adventure10, Mango247
Hi,here is a good one ! please try out! :)
Click to reveal hidden text
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Mateescu Constantin
1842 posts
#9 • 2 Y
Y by Adventure10, Mango247
Another solution
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Dranzer
154 posts
#10 • 5 Y
Y by SHREYAS333, Wizard_32, PME2018, Adventure10, and 1 other user
A pure geometric solution
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
OmkarDivekar
2 posts
#11 • 3 Y
Y by sayanjoddar, Adventure10, Mango247
Sorry for reviving a very old thread !
We have to prove a^2=b(b+c)
Rearranging the terms we get a/b=(b+c)/a
L.H.S:-
By sine rule, a/b=sinA/sinB=2cosB ...(A=2B)
R.H.S:-
By sine rule, (b+c)/a=(sinB+sinC)/sinA=(2sin2B*cosB)/sin2B=2cosB ...(A=2B)
Hence, L.H.S=R.H.S proved.
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
PhysicsMonster_01
1445 posts
#12 • 4 Y
Y by pikazag, MathematicalGiant, Adventure10, Mango247
A bit different solution with the use of trigonometry
This post has been edited 2 times. Last edited by PhysicsMonster_01, Sep 13, 2018, 7:48 AM
Reason: LaTeX
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
LoveMaths26102003
84 posts
#13 • 2 Y
Y by Adventure10, Mango247
Similarity
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
ftheftics
651 posts
#14 • 2 Y
Y by Adventure10, Mango247
Suppose,$\angle B =b'$ ,$\implies \angle A =2b'$,
and,$\angle C =180-3b'$.

See that,$\frac{C}{\sin 3b'} =\frac{b}{\sin b'}$.

$\implies c=b(3-4\sin ^2 b')$.

$\implies c=b(2\cos2b'+1)$.

$\implies c^2 = bc+2bc \cos 2b'$.

Using cosine rule we have ,

$a^2=b^2+c^2 -2bc \cos 2b'$.

$\implies a^2=b^2 +bc$.

As desired.$\boxed{a^2 = b (b+c)}$
This post has been edited 1 time. Last edited by ftheftics, Feb 15, 2020, 12:38 PM
Reason: BNNn
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
sqing
41947 posts
#15 • 1 Y
Y by Adventure10
Rushil wrote:
In a triangle $ABC$, $\angle A = 2 \angle B$. Prove that $a^2 = b (b+c)$.
$$\frac{a}{\sin 2B} = \frac{b}{\sin B}\Leftrightarrow  \frac{a}{ 2b}=cosB=\frac{c^2+a^2-b^2}{ 2ca}
\Leftrightarrow  a^2 = b (b+c)$$
In a triangle $ABC$, $a^2 = b (b+c)$. Prove that $\angle A = 2\angle B.$
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
BestChoice123
1119 posts
#16 • 1 Y
Y by Adventure10
mathmanman wrote:
That's just the law of sines ;)

oops that link failed :(
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
sqing
41947 posts
#17 • 1 Y
Y by Adventure10
BestChoice123 wrote:
mathmanman wrote:
That's just the law of sines ;)

oops that link failed :(
Law_of_Sines
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
S1281
209 posts
#18
Y by
We know that,
$a/sinA=b/sinB=c/sinC$
$a/sin2x=b /sinx=c/sin(180^{\circ{}}-3x)$
$a/2cosx=b$
$c/sin3x=b/sinx$
$c/(3sinx-4sin^3x)=b/sinx$
$c/(3-4sin^2x)=b$
$b(b+c)=b^2+bc=\frac{a^2}{4cos^2x}+\frac{a}{2cosx}(3-4sin^2x)\frac{a}{2cosx}=\frac{a^2}{4 cos^2x}4(1-sin^2x)=\frac{a^2}{4 cos^2x}4cos^2x=a^2$.
This post has been edited 2 times. Last edited by S1281, Apr 19, 2021, 12:13 PM
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
SatisfiedMagma
458 posts
#19
Y by
I was just about the bash thing with trigonometry. But here is a geometric solution I guess.

Solution: Denote $D$ to be the foot of angle bisector of $\angle BAC$ on side $BC$. Now it is easy to notice that $\angle CAD = \angle ABD$. So we can deduce that $AC$ is tangent to $\odot(ADB)$. Applying Power of a Point along with Angle Bisector Theorem we get
\begin{align*}
b^2= \frac{ab}{b+c} \cdot a \\
\implies a^2= b(b+c)
\end{align*}which proves the desired. $\blacksquare$
This post has been edited 2 times. Last edited by SatisfiedMagma, May 14, 2022, 6:57 PM
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Krishijivi
99 posts
#20
Y by
Let angle B=x
Then , angle A=2x
By sine rule,
a/ b=sin 2x/ sin x
cos x =a/2b
cos x=c²+a²-b²/2ac
bc²+ba²-b²-a²c=0
(c-b){b(b+c)-a²}=0
If c=b
Then also a²=b(b+c)
If b(b+c)-a²=0
a²=b(b+c)
@ Krishijivi
Z K Y
N Quick Reply
G
H
=
a