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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
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.

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[*]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]
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0 replies
jlacosta
May 1, 2025
0 replies
2022 MARBLE - Mock ARML I -8 \frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}=32
parmenides51   3
N 6 minutes ago by P162008
Let $a,b,c$ complex numbers with $ab+ +bc+ca = 61$ such that
$$\frac{1}{b+c}+\frac{1}{c+a}+\frac{1}{a+b}= 5$$$$\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}=32.$$Find the value of $abc$.
3 replies
+1 w
parmenides51
Jan 14, 2024
P162008
6 minutes ago
ISI 2025
Zeroin   1
N 19 minutes ago by alexheinis
Let $\mathbb{N}$ denote the set of natural numbers and let $(a_i,b_i),1 \leq i \leq 9$ denote $9$ ordered pairs in $\mathbb{N} \times \mathbb{N}$. Prove that there exist $3$ distinct elements in the set $2^{a_i}3^{b_i}$ for $1 \leq i \leq 9$ whose product is a perfect cube.
1 reply
Zeroin
Yesterday at 2:29 PM
alexheinis
19 minutes ago
Pell's Equation
Entrepreneur   1
N an hour ago by MihaiT
A Pells Equation is defined as follows $$x^2-1=ky^2.$$Where $x,y$ are positive integers and $k$ is a non-square positive integer. If $(x_n,y_n)$ denotes the n-th set of solution to the equation with $(x_0,y_0)=(1,0).$ Then, prove that $$x_{n+1}x_n-ky_{n+1}y_n=x_1,$$$$x_n\pm y_n\sqrt k=(x_1\pm y_1\sqrt k)^n.$$
1 reply
Entrepreneur
2 hours ago
MihaiT
an hour ago
Inequalities
sqing   15
N 2 hours ago by sqing
Let $a,b,c >2 $ and $ ab+bc+ca \leq 75.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 1$$Let $a,b,c >2 $ and $ \frac{1}{a}+\frac{1}{b}+\frac{1}{c}\geq \frac{6}{7}.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 2$$
15 replies
sqing
May 13, 2025
sqing
2 hours ago
Pertenacious Polynomial Problem
BadAtCompetitionMath21420   6
N Today at 3:51 AM by lbh_qys
Let the polynomial $P(x) = x^3-x^2+px-q$ have real roots and real coefficients with $q>0$. What is the maximum value of $p+q$?

This is a problem I made for my math competition, and I wanted to see if someone would double-check my work (No Mike allowed):

solution
Is this solution good?
6 replies
BadAtCompetitionMath21420
May 17, 2025
lbh_qys
Today at 3:51 AM
Vieta's Formula.
BlackOctopus23   4
N Today at 3:11 AM by compoly2010
Can someone help me understand Vieta's Formula? I am currently learning it for my class. I learned that for a polynomial of degree $n$, all the roots added will give $-\frac{a_{n-1}}{a_n}$. I also learned that if every single root, multiplies every single root, it will give $\frac{a_{n-2}}{a_n}$. I also learned that if all the roots are multiplied, it will give $-\frac{a_0}{a_n}$. Is this right? And is there any purpose for these equations?
4 replies
BlackOctopus23
Yesterday at 11:10 PM
compoly2010
Today at 3:11 AM
The sum of 335 distinct positive integers
Streit31415   1
N Today at 12:36 AM by Bocabulary142857
The sum of 335 distinct positive integers is equal to 100000
a) what is the minimum number of odd numbers among them ?
b) what is the maximum number of odd numbers among them ?
1 reply
Streit31415
Yesterday at 11:38 PM
Bocabulary142857
Today at 12:36 AM
Diophantine Equation (cousin of Mordell)
urfinalopp   4
N Yesterday at 10:54 PM by FoeverResentful
Find pairs of integers $(x;y)$ such that:

$x^2=y^5+32$
4 replies
urfinalopp
Yesterday at 6:38 PM
FoeverResentful
Yesterday at 10:54 PM
p+2^p-3=n^2
tom-nowy   1
N Yesterday at 6:51 PM by urfinalopp
Let $n$ be a natural number and $p$ be a prime number. How many different pairs $(n, p)$ satisfy the equation:
$$p + 2^p - 3 = n^2 .$$
Inspired by https://artofproblemsolving.com/community/c4h3560823
1 reply
tom-nowy
Yesterday at 11:16 AM
urfinalopp
Yesterday at 6:51 PM
Perfect cubes
Entrepreneur   6
N Yesterday at 6:23 PM by NamelyOrange
Find all ordered pairs of positive integers $(a,b,c)$ such that $\overline{abc}$ and $\overline{cab}$ are both perfect cubes.
6 replies
Entrepreneur
Yesterday at 6:04 PM
NamelyOrange
Yesterday at 6:23 PM
Ez comb proposed by ME
IEatProblemsForBreakfast   1
N Yesterday at 3:09 PM by n1g3r14n
A and B play a game on two table:
1.At first one table got $n$ different coloured marbles on it and another one is empty
2.At each move player choose set of marbles that hadn't choose either players before and all chosen marbles from same table, and move all the marbles in that set to another table
3.Player who can not move lose
If A starts and they move alternatily who got the winning strategy?
1 reply
IEatProblemsForBreakfast
Yesterday at 9:02 AM
n1g3r14n
Yesterday at 3:09 PM
geometry
luckvoltia.112   0
Yesterday at 3:04 PM
ChGiven an acute triangle ABC inscribed in circle $(O)$ The altitudes $BE, CF$ , intersect
each other at $H$. The tangents at $B$ and $C $of $(O)$ intersect at $S$. Let $M $be the midpoint of $BC$. $EM$ intersects $SC$
at $I$, $FM$ intersects $SB$ at $J.$
a) Prove that the points $I, S, M, J$ lie on the same circle.
b) The circle with diameter $AH$ intersects the circle $(O)$ at the second point $T.$ The line $AH$ intersects
$(O)$ at the second point $K$. Prove that $S,K,T$ are collinear.
0 replies
luckvoltia.112
Yesterday at 3:04 PM
0 replies
Exponents of integer question
Dheckob   4
N Yesterday at 2:45 PM by LeYohan
Find the smallest positive integer $m$ such that $5m$ is an exact 5th power, $6m$ is an exact 6th power, and $7m$ is an exact 7th power.
4 replies
Dheckob
Apr 12, 2017
LeYohan
Yesterday at 2:45 PM
Inequalities
sqing   3
N Yesterday at 1:49 PM by sqing
Let $ a,b>0   $ . Prove that
$$ \frac{a}{a^2+a +2b+1}+ \frac{b}{b^2+2a +b+1}  \leq  \frac{2}{5} $$$$ \frac{a}{a^2+2a +b+1}+ \frac{b}{b^2+a +2b+1}  \leq  \frac{2}{5} $$
3 replies
sqing
May 13, 2025
sqing
Yesterday at 1:49 PM
trigonometric functions
VivaanKam   16
N May 16, 2025 by Shan3t
Hi could someone explain the basic trigonometric functions to me like sin, cos, tan etc.
Thank you!
16 replies
VivaanKam
Apr 29, 2025
Shan3t
May 16, 2025
trigonometric functions
G H J
G H BBookmark kLocked kLocked NReply
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VivaanKam
167 posts
#1 • 2 Y
Y by PikaPika999, linjiah
Hi could someone explain the basic trigonometric functions to me like sin, cos, tan etc.
Thank you!
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Lijin
225 posts
#2 • 2 Y
Y by PikaPika999, linjiah
Are you talking about graphing them or just the basic ratios?
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Yiyj1
1266 posts
#4 • 2 Y
Y by PikaPika999, linjiah
Basic ratios: draw a right triangle. I'm terrible at asy so i can't draw one D:. Anyways, label one of the angles $\theta$. Then, label the hypotenuse with $H$, the leg adjacent to $\theta$ as $A$ (for adjacent) and the other leg $O$ (for opposite). Then, just remember this: SOH CAH TOA:\[\sin\theta=\dfrac{O}{H}, \cos\theta=\dfrac{A}{H}, \tan\theta=\dfrac{O}{A}.\]Then there are like $\sec, \csc, \cot$, which are the reciprocals of $\cos, \sin, \tan$. IMPORTANT: $\sec$ is the reciprocal of $\cos$ and $\csc$ is the reciprocal of $\sin$, not the other way around.
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aok
350 posts
#5 • 1 Y
Y by linjiah
To solve things such as $\sin 150$ or $\cos 270$ you can draw a circle of radius 1 around the origin, rotate a line from the positive x line counterclockwise by $\theta^\circ$ to form a new line. To solve for cos,sin, and tan $\theta,$ where the $(x,y)$ hits circle after rotation and $x = \cos\theta$,$y = \sin\theta$, and $\frac{y}{x} = \tan\theta.$
This post has been edited 4 times. Last edited by aok, Apr 29, 2025, 10:48 PM
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VivaanKam
167 posts
#6 • 1 Y
Y by linjiah
Yiyj1 wrote:
Basic ratios: draw a right triangle. I'm terrible at asy so i can't draw one D:. Anyways, label one of the angles $\theta$. Then, label the hypotenuse with $H$, the leg adjacent to $\theta$ as $A$ (for adjacent) and the other leg $O$ (for opposite). Then, just remember this: SOH CAH TOA:\[\sin\theta=\dfrac{O}{H}, \cos\theta=\dfrac{A}{H}, \tan\theta=\dfrac{O}{A}.\]Then there are like $\sec, \csc, \cot$, which are the reciprocals of $\cos, \sin, \tan$. IMPORTANT: $\sec$ is the reciprocal of $\cos$ and $\csc$ is the reciprocal of $\sin$, not the other way around.

So like this?

[asy]

draw((0,0)--(3,0)--(0,2)--cycle);
label("$\theta$", (2.7,0.1),W);
label("$A$", (1.5,0), S);
label("$O$", (0,1.205), W);
label("$H$", (1.2,1.1), NE);
[/asy]
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VivaanKam
167 posts
#7 • 1 Y
Y by linjiah
That’s cool! So if you have the lengths of a triangle you can find its angles?
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VivaanKam
167 posts
#8 • 1 Y
Y by linjiah
aok wrote:
To solve things such as $\sin 150$ or $\cos 270$ you can draw a circle of radius 1 around the origin, rotate a line from the positive x line counterclockwise by $\theta^\circ$ to form a new line. To solve for cos,sin, and tan $\theta,$ where the $(x,y)$ hits circle after rotation and $x = \cos\theta$,$y = \sin\theta$, and $\frac{y}{x} = \tan\theta.$

are they like polar quardinits ?
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VivaanKam
167 posts
#9 • 1 Y
Y by linjiah
but the wouldn't $\cos x$ have 2 values because on a circle there are two quordinates with the same $x$ position?
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lpieleanu
3001 posts
#10 • 1 Y
Y by linjiah
Yes, you can find the side lengths of a triangle given its angles. (If it is right, you can just use the standard ratio definitions of $\sin, \cos, \tan$ and use inverse trigonometric functions, and if it is not right, then you can use the Law of Cosines to find each angle.)

The point in rectangular coordinates $(\cos(\theta), \sin(\theta))$ corresponds to the point in polar coordinates $(1, \theta),$ i.e. $(\cos(\theta), \sin(\theta))$ is the point on the unit circle at an angle of $\theta$ radians counterclockwise of the positive $x$-axis.

Yes, the equation $\cos(x)=a$ has two solutions in $[0, 2\pi)$ for all $-1<a<1.$

Also, reminder that you can combine all of your questions into the same post. :)
This post has been edited 1 time. Last edited by lpieleanu, Apr 30, 2025, 6:39 PM
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aok
350 posts
#11 • 1 Y
Y by linjiah
that is correct, cos x = a has 2 solutions (generally)
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aok
350 posts
#12 • 1 Y
Y by linjiah
for x btw
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aok
350 posts
#13 • 1 Y
Y by linjiah
VivaanKam wrote:
That’s cool! So if you have the lengths of a triangle you can find its angles?

Correct, use the opposite of those functions.
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aok
350 posts
#14 • 1 Y
Y by linjiah
*use the cos theorem to find cos(x) then use the cos^-1
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BlackOctopus23
143 posts
#15 • 1 Y
Y by linjiah
The Unit Circle is also vital in trigonometry and in understanding the functions. This video helped me understand it a lot! Click to reveal hidden text. The unit circle is basically a circle of radius one. Remember that $cos$ is the $x$ and $sin$ is the $y$ if we are viewing it in the perspective of a graph.
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aok
350 posts
#16
Y by
Using unit circle as stated.
aok wrote:
To solve things such as $\sin 150$ or $\cos 270$ you can draw a circle of radius 1 around the origin, rotate a line from the positive x line counterclockwise by $\theta^\circ$ to form a new line. To solve for cos,sin, and tan $\theta,$ where the $(x,y)$ hits circle after rotation and $x = \cos\theta$,$y = \sin\theta$, and $\frac{y}{x} = \tan\theta.$
This post has been edited 1 time. Last edited by aok, May 16, 2025, 12:42 AM
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Shan3t
393 posts
#17
Y by
might be a bit advanced but Ceva's Theorem, and Extended LoS
This post has been edited 1 time. Last edited by Shan3t, May 16, 2025, 1:03 AM
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Shan3t
393 posts
#18
Y by
Shan3t wrote:
might be a bit advanced but Ceva's Theorem, and Extended LoS

also SAS(for area, side angle side), and Ceva's branches off to Menelaus's
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