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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.

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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]
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0 replies
jlacosta
Apr 2, 2025
0 replies
k i Adding contests to the Contest Collections
dcouchman   1
N Apr 5, 2023 by v_Enhance
Want to help AoPS remain a valuable Olympiad resource? Help us add contests to AoPS's Contest Collections.

Find instructions and a list of contests to add here: https://artofproblemsolving.com/community/c40244h1064480_contests_to_add
1 reply
dcouchman
Sep 9, 2019
v_Enhance
Apr 5, 2023
k i Zero tolerance
ZetaX   49
N May 4, 2019 by NoDealsHere
Source: Use your common sense! (enough is enough)
Some users don't want to learn, some other simply ignore advises.
But please follow the following guideline:


To make it short: ALWAYS USE YOUR COMMON SENSE IF POSTING!
If you don't have common sense, don't post.


More specifically:

For new threads:


a) Good, meaningful title:
The title has to say what the problem is about in best way possible.
If that title occured already, it's definitely bad. And contest names aren't good either.
That's in fact a requirement for being able to search old problems.

Examples:
Bad titles:
- "Hard"/"Medium"/"Easy" (if you find it so cool how hard/easy it is, tell it in the post and use a title that tells us the problem)
- "Number Theory" (hey guy, guess why this forum's named that way¿ and is it the only such problem on earth¿)
- "Fibonacci" (there are millions of Fibonacci problems out there, all posted and named the same...)
- "Chinese TST 2003" (does this say anything about the problem¿)
Good titles:
- "On divisors of a³+2b³+4c³-6abc"
- "Number of solutions to x²+y²=6z²"
- "Fibonacci numbers are never squares"


b) Use search function:
Before posting a "new" problem spend at least two, better five, minutes to look if this problem was posted before. If it was, don't repost it. If you have anything important to say on topic, post it in one of the older threads.
If the thread is locked cause of this, use search function.

Update (by Amir Hossein). The best way to search for two keywords in AoPS is to input
[code]+"first keyword" +"second keyword"[/code]
so that any post containing both strings "first word" and "second form".


c) Good problem statement:
Some recent really bad post was:
[quote]$lim_{n\to 1}^{+\infty}\frac{1}{n}-lnn$[/quote]
It contains no question and no answer.
If you do this, too, you are on the best way to get your thread deleted. Write everything clearly, define where your variables come from (and define the "natural" numbers if used). Additionally read your post at least twice before submitting. After you sent it, read it again and use the Edit-Button if necessary to correct errors.


For answers to already existing threads:


d) Of any interest and with content:
Don't post things that are more trivial than completely obvious. For example, if the question is to solve $x^{3}+y^{3}=z^{3}$, do not answer with "$x=y=z=0$ is a solution" only. Either you post any kind of proof or at least something unexpected (like "$x=1337, y=481, z=42$ is the smallest solution). Someone that does not see that $x=y=z=0$ is a solution of the above without your post is completely wrong here, this is an IMO-level forum.
Similar, posting "I have solved this problem" but not posting anything else is not welcome; it even looks that you just want to show off what a genius you are.

e) Well written and checked answers:
Like c) for new threads, check your solutions at least twice for mistakes. And after sending, read it again and use the Edit-Button if necessary to correct errors.



To repeat it: ALWAYS USE YOUR COMMON SENSE IF POSTING!


Everything definitely out of range of common sense will be locked or deleted (exept for new users having less than about 42 posts, they are newbies and need/get some time to learn).

The above rules will be applied from next monday (5. march of 2007).
Feel free to discuss on this here.
49 replies
ZetaX
Feb 27, 2007
NoDealsHere
May 4, 2019
P(x) | P(x^2-2)
GreenTea2593   4
N an hour ago by GreenTea2593
Source: Valentio Iverson
Let $P(x)$ be a monic polynomial with complex coefficients such that there exist a polynomial $Q(x)$ with complex coefficients for which \[P(x^2-2)=P(x)Q(x).\]Determine all complex numbers that could be the root of $P(x)$.

Proposed by Valentio Iverson, Indonesia
4 replies
GreenTea2593
3 hours ago
GreenTea2593
an hour ago
USEMO P6 (Idk what to say here)
franzliszt   16
N an hour ago by MathLuis
Source: USEMO 2020/6
Prove that for every odd integer $n > 1$, there exist integers $a, b > 0$ such that, if we let $Q(x) = (x + a)^
2 + b$, then the following conditions hold:
$\bullet$ we have $\gcd(a, n) = gcd(b, n) = 1$;
$\bullet$ the number $Q(0)$ is divisible by $n$; and
$\bullet$ the numbers $Q(1), Q(2), Q(3), \dots$ each have a prime factor not dividing $n$.
16 replies
+1 w
franzliszt
Oct 25, 2020
MathLuis
an hour ago
Prove that the fraction (21n + 4)/(14n + 3) is irreducible
DPopov   110
N an hour ago by Shenhax
Source: IMO 1959 #1
Prove that the fraction $ \dfrac{21n + 4}{14n + 3}$ is irreducible for every natural number $ n$.
110 replies
DPopov
Oct 5, 2005
Shenhax
an hour ago
Let \( a, b, c \) be positive real numbers satisfying \[ a^2 + c^2 = b(a + c). \
Jackson0423   3
N an hour ago by Mathzeus1024
Let \( a, b, c \) be positive real numbers satisfying
\[
a^2 + c^2 = b(a + c).
\]Let
\[
m = \min \left( \frac{a^2 + ab + b^2}{ab + bc + ca} \right).
\]Find the value of \( 2024m \).
3 replies
Jackson0423
Apr 16, 2025
Mathzeus1024
an hour ago
real+ FE
pomodor_ap   3
N 2 hours ago by MathLuis
Source: Own, PDC001-P7
Let $f : \mathbb{R}^+ \to \mathbb{R}^+$ be a function such that
$$f(x)f(x^2 + y f(y)) = f(x)f(y^2) + x^3$$for all $x, y \in \mathbb{R}^+$. Determine all such functions $f$.
3 replies
pomodor_ap
Yesterday at 11:24 AM
MathLuis
2 hours ago
Inspired by hlminh
sqing   1
N 2 hours ago by sqing
Source: Own
Let $ a,b,c $ be real numbers such that $ a^2+b^2+c^2=1. $ Prove that $$ |a-kb|+|b-kc|+|c-ka|\leq \sqrt{3k^2+2k+3}$$Where $ k\geq 0 . $
1 reply
sqing
2 hours ago
sqing
2 hours ago
1234th Post!
PikaPika999   138
N 2 hours ago by martianrunner
I hit my 1234th post! (I think I missed it, I'm kinda late, :oops_sign:)

But here's a puzzle for you all! Try to create the numbers 1 through 25 using the numbers 1, 2, 3, and 4! You are only allowed to use addition, subtraction, multiplication, division, and parenthesis. If you're post #1, try to make 1. If you're post #2, try to make 2. If you're post #3, try to make 3, and so on. If you're a post after 25, then I guess you can try to make numbers greater than 25 but you can use factorials, square roots, and that stuff. Have fun!

1: $(4-3)\cdot(2-1)$
138 replies
PikaPika999
Yesterday at 8:54 PM
martianrunner
2 hours ago
Website to learn math
hawa   39
N 2 hours ago by xHypotenuse
Hi, I'm kinda curious what website do yall use to learn math, like i dont find any website thats fun to learn math
39 replies
hawa
Apr 9, 2025
xHypotenuse
2 hours ago
Is this FE solvable?
ItzsleepyXD   3
N 2 hours ago by jasperE3
Source: Original
Let $c_1,c_2 \in \mathbb{R^+}$. Find all $f : \mathbb{R^+} \rightarrow \mathbb{R^+}$ such that for all $x,y \in \mathbb{R^+}$ $$f(x+c_1f(y))=f(x)+c_2f(y)$$
3 replies
ItzsleepyXD
Yesterday at 3:02 AM
jasperE3
2 hours ago
PQ bisects AC if <BCD=90^o, A, B,C,D concyclic
parmenides51   2
N 2 hours ago by venhancefan777
Source: Mathematics Regional Olympiad of Mexico Northeast 2020 P2
Let $A$, $B$, $C$ and $D$ be points on the same circumference with $\angle BCD=90^\circ$. Let $P$ and $Q$ be the projections of $A$ onto $BD$ and $CD$, respectively. Prove that $PQ$ cuts the segment $AC$ into equal parts.
2 replies
parmenides51
Sep 7, 2022
venhancefan777
2 hours ago
Inequality with three conditions
oVlad   3
N 2 hours ago by sqing
Source: Romania EGMO TST 2019 Day 1 P3
Let $a,b,c$ be non-negative real numbers such that \[b+c\leqslant a+1,\quad c+a\leqslant b+1,\quad a+b\leqslant c+1.\]Prove that $a^2+b^2+c^2\leqslant 2abc+1.$
3 replies
1 viewing
oVlad
Yesterday at 1:48 PM
sqing
2 hours ago
standard Q FE
jasperE3   2
N 2 hours ago by jasperE3
Source: gghx, p19004309
Find all functions $f:\mathbb Q\to\mathbb Q$ such that for any $x,y\in\mathbb Q$:
$$f(xf(x)+f(x+2y))=f(x)^2+f(y)+y.$$
2 replies
jasperE3
Sunday at 6:27 PM
jasperE3
2 hours ago
bracelets
pythagorazz   5
N 3 hours ago by That_One_Genius.
Kat designs circular bead bracelets for kids. Each bracelet has 5 beads, all of which are either yellow or green. If beads of the same color are identical, how many distinct bracelets could Kat make?
5 replies
pythagorazz
Apr 14, 2025
That_One_Genius.
3 hours ago
2025 MATHCOUNTS State Hub
SirAppel   589
N 5 hours ago by CXP
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 34? 34? 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!
589 replies
SirAppel
Apr 1, 2025
CXP
5 hours ago
two solutions
τρικλινο   10
N Apr 14, 2025 by Safal
in a book:CORE MATHS for A-LEVEL ON PAGE 41 i found the following


1st solution


$x^2-5x=0$



$ x(x-5)=0$



hence x=0 or x=5



2nd solution



$x^2-5x=0$

$x-5=0$ dividing by x



hence the solution x=0 has been lost



is the above correct?
10 replies
τρικλινο
Apr 12, 2025
Safal
Apr 14, 2025
two solutions
G H J
G H BBookmark kLocked kLocked NReply
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τρικλινο
502 posts
#1
Y by
in a book:CORE MATHS for A-LEVEL ON PAGE 41 i found the following


1st solution


$x^2-5x=0$



$ x(x-5)=0$



hence x=0 or x=5



2nd solution



$x^2-5x=0$

$x-5=0$ dividing by x



hence the solution x=0 has been lost



is the above correct?
Z K Y
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Safal
168 posts
#2
Y by
2nd Solution is basically wrong. Why? Here is the explanation.

$$x(x-5)=0$$Then there are two cases either $x=0$ or $x\neq 0$.When we are admitting the case $x=0$ we cannot divide by $0$. So, in the case we apply divison by $x$ then $x\neq 0$ is a solid prerequisite to do so.Thus, $x-5=0$ from $x(x-5)=0$ we must take the assumption in hand that $x\neq 0$. For example take the extension of the same problem in $\mathbb{F}_5$ then the same problem reads $$x^2=0$$,implying only one solution with optimistic repetation of root $0$, two times that is the multiplicity of $0$ in $x^2$. Thankfully, we are lucky enough that we are in the field of $\text{char}$ $0$.The reason is that, the book you mention was a book for below 10std (as far as I remember it is below 10th std) students, where prerequisite assumption is that ,we should work on field of $\text{char}$ $0$.
This post has been edited 10 times. Last edited by Safal, Apr 12, 2025, 7:52 PM
Z K Y
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τρικλινο
502 posts
#3
Y by
Safal wrote:
2nd Solution is basically wrong. Why? Here is the explanation.

$$x(x-5)=0$$Then there are two cases either $x=0$ or $x\neq 0$.When we are admitting the case $x=0$ we cannot divide by $0$. So, in the case we apply divison by $x$ then $x\neq 0$ is a solid prerequisite to do so.Thus, $x-5=0$ from $x(x-5)=0$ we must take the assumption in hand that $x\neq 0$. For example take the extension of the same problem in $\mathbb{F}_5$ then the same problem reads $$x^2=0$$,implying only one solution with optimistic repetation of root $0$, two times that is the multiplicity of $0$ in $x^2$. Thankfully, we are lucky enough that we are in the field of $\text{char}$ $0$.The reason is that, the book you mention was a book for below 10std (as far as I remember it is below 10th std) students, where prerequisite assumption is that ,we should work on field of $\text{char}$ $0$.

so how do we get x=0 or x=5 ,since we assumed $x\neq 0$.
Z K Y
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maxamc
552 posts
#4
Y by
Move this to MSM, reported
Z K Y
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Safal
168 posts
#5
Y by
τρικλινο wrote:
Safal wrote:
2nd Solution is basically wrong. Why? Here is the explanation.

$$x(x-5)=0$$Then there are two cases either $x=0$ or $x\neq 0$.When we are admitting the case $x=0$ we cannot divide by $0$. So, in the case we apply divison by $x$ then $x\neq 0$ is a solid prerequisite to do so.Thus, $x-5=0$ from $x(x-5)=0$ we must take the assumption in hand that $x\neq 0$. For example take the extension of the same problem in $\mathbb{F}_5$ then the same problem reads $$x^2=0$$,implying only one solution with optimistic repetation of root $0$, two times that is the multiplicity of $0$ in $x^2$. Thankfully, we are lucky enough that we are in the field of $\text{char}$ $0$.The reason is that, the book you mention was a book for below 10std (as far as I remember it is below 10th std) students, where prerequisite assumption is that ,we should work on field of $\text{char}$ $0$.

so how do we get x=0 or x=5 ,since we assumed $x\neq 0$.

If you read carefully I haven't said that we cannot get $x=0$.The assumption whenever $x\neq 0$ we get $x=5$ else we get the case $x=0$.I can explain you more but the fact is I cannot use argument of field theory to explain it in total details.The reason why it's actually the case lies in field theory logics.
This post has been edited 1 time. Last edited by Safal, Apr 13, 2025, 6:23 AM
Z K Y
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τρικλινο
502 posts
#6
Y by
what is field theory logic.
IS the logic that suports the development of field theory?
THIS post should not be moved to Middle School Math
Because in the 2nd solution we have the answer : x different than zero this implies x=5
And according to logic this is equivelant to x=0 or x=5.Hence no solution is lost as the book claims
There for it should be removed back to at least college algebra although i doupt if even there anyone knew of that solution
WEmake use of the law of propositional calculus: ¬p implies q this is equivelant to p or q
Z K Y
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Safal
168 posts
#7
Y by
"If you judge a fish because it cannot climb a tree , it will be foolish"-Unknown.

I am not commenting further in this post thank you.

Thanks to aops for moving it to MSM and I support it.
This post has been edited 1 time. Last edited by Safal, Apr 13, 2025, 4:51 PM
Z K Y
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SpeedCuber7
1814 posts
#8
Y by
@triklino dude that's an awesome username i didn't even know greek letters were allowed lol
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sadas123
1231 posts
#9
Y by
Proof: $x^2-5x=0$ Which means that the roots of this equation have to be real so we can use an method that is lost in the darkness called factoring. We can factor out the $x$ from each of the terms on the left hand side and get $x(x-5)=0$ which with more logic we can find that the possible outcomes is that if the Parantheses are 0 or the x=0 so first we can subsitute a value of x into that to make the value 0 so we get that x=5 and we finally get the solutions of $x=5$ and $x=0$ and to wrap up our proof we can prove that factoring is the best way to go because with quadratics you would only find 2 possibiliteis or 1 depending on the plus minus. And the other thing is that if you divide by x and just solve it with algebra then you will only get the solution of 5. Thus, proving that factoring is the best method out of all of them. We can use the remainder theorem to prove this which can be done easily. $\blacksquare$
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τρικλινο
502 posts
#10
Y by
please read the previous posts


The question here is not which is the best method to solve the problem,but if we lose a solution if we solve the problem by dividing the equation by a non zero x
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Safal
168 posts
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Dear Triklino , I am high yesterday I am sorry for being rude. Can you please explain your Question properly that is what the thing you exactly want to know. According to what I understand, you wanted to know why in 2nd Solution $x=0$ is lost? right. Well forget about field theory and all that, Let me explain it in layman's term what is actually happening. In second solution , the solution $x=0$ is not actually lost. The reason we are getting $x=5$ but not $x=0$ is beacuse when we are dividing by $x$ we making an assumption that $x\neq 0$ and since we are making this assumption the solution $x=0$ is lost. For example when we divide by $x-5$ the solution $x=5$ is lost why $x-5=y(say)$ and we are assuming $y\neq 0$ which is equivalent to $x\neq 5$. Now divison by zero is not possible which is not at all very easy to explain. Now $x=5$ and $x=0$ is not possible at the same time. Thus either $x=0$ or $x=5$.

Now why I am talking about field beacuse $0$ and $5$ can be same when we are in a field of $\text{char} 5$. If you are avoid knowing what is field that's perfectly fine to learn later, but just in layman's term note that $0=5$ is possible in finite fields of charecteristic $5$.

Well I like sour grapes but fox will be happy if he clear your doubt thanks.

I hope it is clear now. If it is not then text me in dm.
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