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Ratio of lengths
Sadigly   1
N 42 minutes ago by Frd_19_Hsnzde
In a triangle $ABC$, $I$ is the incenter. Line $CI$ intersects circumcircle of $ABC$ at $L$, and it is given that $CI=2IL$. $M;N$ are points chosen on $AB$ such that $\angle AIM=\angle BIN=90$. Prove that $AB=2MN$
1 reply
Sadigly
2 hours ago
Frd_19_Hsnzde
42 minutes ago
Stylish Numbers
pedronis   0
4 hours ago
A positive even integer $n$ is called stylish if the set $\{1, 2, \ldots, n\}$ can be partitioned into $\frac{n}{2}$ pairs such that the sum of the elements in each pair is a power of $3$. For example, $6$ is stylish because the set $\{1, 2, 3, 4, 5, 6\}$ can be partitioned as $\{1,2\}, \{3,6\}, \{4,5\}$, with sums $3$, $9$, and $9$ respectively. Determine the number of stylish numbers less than $3^{2025}$.
0 replies
pedronis
4 hours ago
0 replies
New geometry problem
titaniumfalcon   4
N 5 hours ago by titaniumfalcon
Post any solutions you have, with explanation or proof if possible, good luck!
4 replies
titaniumfalcon
Apr 3, 2025
titaniumfalcon
5 hours ago
A rather difficult question
BeautifulMath0926   1
N 5 hours ago by jasperE3
I got a difficult equation for users to solve:
Find all functions f: R to R, so that to all real numbers x and y,
1+f(x)f(y)=f(x+y)+f(xy)+xy(x+y-2) holds.
1 reply
BeautifulMath0926
Today at 11:10 AM
jasperE3
5 hours ago
Combinatorics.
NeileshB   0
5 hours ago
An odd integer is written in each cell of a 2009  2009 table. For 1  i  2009 let Ri be
the sum of the numbers in the ith row, and for 1  j  2009 let Cj be the sum of the
numbers in the jth column. Finally, let A be the product of the Ri, and B the product of
the Cj . Prove that A + B is different from zero.

I really need help on this. Can people give me hints? I don’t know where to start.
0 replies
NeileshB
5 hours ago
0 replies
how many quadrilaterals ?
Ecrin_eren   0
6 hours ago
"All the diagonals of an 11-gon are drawn. How many quadrilaterals can be formed using these diagonals as sides? (The vertices of the quadrilaterals are selected from the vertices of the 11-gon.)"
0 replies
Ecrin_eren
6 hours ago
0 replies
NC State Math Contest Wake Tech Regional Problems and Solutions
mathnerd_101   10
N Today at 2:51 PM by mathnerd_101
Problem 1: Determine the area enclosed by the graphs of $$y=|x-2|+|x-4|-2, y=-|x-3|+4.$$ Hint
Solution to P1

Problem 2: Calculate the sum of the real solutions to the equation $x^\frac{3}{2} -9x-16x^\frac{1}{2} +144=0.$
Hint
Solution to P2



Problem 3: List the two transformations needed to convert the graph $\frac{x-1}{x+2}$ to $\frac{3x-6}{x-1}.$
Hint
Solution to P3

Problem 4: Let $a,b$ be positive real numbers such that $a^2-b^2=20,$ and $a^3-b^3=120.$ Determine the value of $a+\frac{b^2}{a+b}.$
Hint
Solution for P4

Problem 5: Eve and Oscar are playing a game where they roll a fair, six-sided die. If an even number occurs on two consecutive rolls, then Eve wins. If an odd number is immediately followed by an even number, Oscar wins. The die is rolled until one person wins. What is the probability that Oscar wins?
Hint
Solution to P5

Problem 6: In triangle $ABC,$ $M$ is on point $\overline{AB}$ such that $AM = x+32$ and $MB=x+12$ and $N$ is a point on $\overline{AC}$ such that $MN=2x+1$ and $BC=x+22.$ Given that $\overline{MN} || \overline{BC},$ calculate $MN.$
Hint
Solution to P6

Problem 7: Determine the sum of the zeroes of the quadratic of polynomial $Q(x),$ given that $$Q(0)=72, Q(1) = 75, Q(3) = 63.$$
Hint

Solution to Problem 7

Problem 8:
Hint
Solution to P8

Problem 9:
Find the sum of all real solutions to $$(x-4)^{log_8(4x-16)} = 2.$$ Hint
Solution to P9

Problem 10:
Define the function
\[f(x) = 
\begin{cases} 
x - 9, & \text{if } x > 100 \\ 
f(f(x + 10)), & \text{if } x \leq 100 
\end{cases}\]
Calculate \( f(25) \).

Hint

Solution to P10

Problem 11:
Let $a,b,x$ be real numbers such that $$log_{a-b} (a+b) = 3^{a+b}, log_{a+b} (a-b) = 125 \cdot 15^{b-a}, a^2-b^2=3^x. $$Find $x.$
Hint

Solution to P11

Problem 12: Points $A,B,C$ are on circle $Q$ such that $AC=2,$ $\angle AQC = 180^{\circ},$ and $\angle QAB = 30^{\circ}.$ Determine the path length from $A$ to $C$ formed by segment $AB$ and arc $BC.$

Hint
Solution to P12

Problem 13: Determine the number of integers $x$ such that the expression $$\frac{\sqrt{522-x}}{\sqrt{x-80}} $$is also an integer.
Hint

Solution to Problem 13

Problem 14: Determine the smallest positive integer $n$ such that $n!$ is a multiple of $2^15.$

Hint
Solution to Problem 14

Problem 15: Suppose $x$ and $y$ are real numbers such that $x^3+y^3=7,$ and $xy(x+y)=-2.$ Calculate $x-y.$
Funnily enough, I guessed this question right in contest.

Hint
Solution to Problem 15

Problem 16: A sequence of points $p_i = (x_i, y_i)$ will follow the rules such that
\[
p_1 = (0,0), \quad p_{i+1} = (x_i + 1, y_i) \text{ or } (x_i, y_i + 1), \quad p_{10} = (4,5).
\]How many sequences $\{p_i\}_{i=1}^{10}$ are possible such that $p_1$ is the only point with equal coordinates?

Hint
Solution to P16

Problem 18: (Also stolen from akliu's blog post)
Calculate

$$\sum_{k=0}^{11} (\sqrt{2} \sin(\frac{\pi}{4}(1+2k)))^k$$
Hint
Solution to Problem 18

Problem 19: Determine the constant term in the expansion of $(x^3+\frac{1}{x^2})^{10}.$

Hint
Solution to P19

Problem 20:

In a magical pond there are two species of talking fish: trout, whose statements are always true, and \emph{flounder}, whose statements are always false. Six fish -- Alpha, Beta, Gamma, Delta, Epsilon, and Zeta -- live together in the pond. They make the following statements:
Alpha says, "Delta is the same kind of fish as I am.''
Beta says, "Epsilon and Zeta are different from each other.''
Gamma says, "Alpha is a flounder or Beta is a trout.''
Delta says, "The negation of Gamma's statement is true.''
Epsilon says, "I am a trout.''
Zeta says, "Beta is a flounder.''

How many of these fish are trout?

Hint
Solution to P20
SHORT ANSWER QUESTIONS:
1. Five people randomly choose a positive integer less than or equal to $10.$ The probability that at least two people choose the same number can be written as $\frac{m}{n}.$ Find $m+n.$

Hint
Solution to S1

2. Define a function $F(n)$ on the positive integers using the rule that for $n=1,$ $F(n)=0.$ For all prime $n$, $F(n) = 1,$ and for all other $n,$ $F(xy)=xF(y) + yF(x).$ Find the smallest possible value of $n$ such that $F(n) = 2n.$

Hint
Solution to S2

3. How many integers $n \le 2025$ can be written as the sum of two distinct, non-negative integer powers of $3?$
Huge shoutout to OTIS for teaching me how to solve problems like this.

Hint

Solution to S3

4. Let $S$ be the set of positive integers of $x$ such that $x^2-5y^2=1$ for some other positive integer $y.$ Find the only three-digit value of $x$ in $S.$
Hint
Solution to S4

5. Let $N$ be a positive integer and let $M$ be the integer that is formed by removing the first three digits from $N.$ Find the value of $N$ with least value such that $N = 2025M.$
Hint

Solution to S5
10 replies
mathnerd_101
Apr 11, 2025
mathnerd_101
Today at 2:51 PM
fractional part
Ecrin_eren   0
Today at 2:51 PM
{x^2}+{x}=0.64

How many positive real values of x satisfy this equation?
0 replies
Ecrin_eren
Today at 2:51 PM
0 replies
Problem of power of 2
nhathhuyyp5c   0
Today at 2:18 PM
Let $a,b,c$ be odd positive integers such that $a>b$ and both $a^2+c$ and $b^2+c$ are powers of 2. Prove that $ac>2b^2.$
0 replies
nhathhuyyp5c
Today at 2:18 PM
0 replies
geometry parabola problem
smalkaram_3549   10
N Today at 2:05 PM by ReticulatedPython
How would you solve this without using calculus?
10 replies
smalkaram_3549
Friday at 9:52 PM
ReticulatedPython
Today at 2:05 PM
number of contestants
Ecrin_eren   0
Today at 2:01 PM




In a mathematics competition with 10 questions, every group of 3 questions is solved by more than half of the participants. No participant has solved any 7 questions. Exactly one participant has solved 6 questions. What could be the number of participants?
1994
2000
2013
2048
None of the above
0 replies
Ecrin_eren
Today at 2:01 PM
0 replies
Not so classic orthocenter problem
m4thbl3nd3r   6
N Mar 29, 2025 by maths_enthusiast_0001
Source: own?
Let $O$ be circumcenter of a non-isosceles triangle $ABC$ and $H$ be a point in the interior of $\triangle ABC$. Let $E,F$ be foots of perpendicular lines from $H$ to $AC,AB$. Suppose that $BCEF$ is cyclic and $M$ is the circumcenter of $BCEF$, $HM\cap AB=K,AO\cap BE=T$. Prove that $KT$ bisects $EF$
6 replies
m4thbl3nd3r
Mar 28, 2025
maths_enthusiast_0001
Mar 29, 2025
Not so classic orthocenter problem
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m4thbl3nd3r
276 posts
#1 • 1 Y
Y by ehuseyinyigit
Let $O$ be circumcenter of a non-isosceles triangle $ABC$ and $H$ be a point in the interior of $\triangle ABC$. Let $E,F$ be foots of perpendicular lines from $H$ to $AC,AB$. Suppose that $BCEF$ is cyclic and $M$ is the circumcenter of $BCEF$, $HM\cap AB=K,AO\cap BE=T$. Prove that $KT$ bisects $EF$
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MathLuis
1487 posts
#2 • 1 Y
Y by Funcshun840
You can actually MMP this twice and since its late I'll only give a sketch.
Let $A'$ antipode of $A$ on $\triangle ABC$ then $H,M,A'$ can be easly MMP'd as $H,M$ boh have degree one by simply checking where your cases are $F=B, E=C, E=F=A$ and $H$ orthocenter. Now from this notice $K$ also has degree one snd so does $T$ now which means that $K,N,T$ colinear is degree 4 and the cases are $E=A, E=C, F=B$ and $H$ orthocenter of $\triangle ABC$, where on this case its just trivial by Pascal on $(AH)$ so you are done.
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pingupignu
48 posts
#3
Y by
Let $Q = (AEF) \cap (ABC)$ which is the Miquel point of $BFEC$. Note that $\angle MQA = 90$ so $MHQ$ collinear and passes through the $A$ antipode $Z$. From Menelaus theorem it suffices to show $$\frac{BT}{TE} = \frac{BK}{KF}$$Note that $$\frac{BT}{TE} = \frac{BA}{AE} \cdot \frac{BZ}{CZ} = \frac{BA}{AE} \cdot \frac{EH}{HF}$$and
$$\frac{BK}{KF} = \frac{BH}{HF} \cdot \frac{\sin \angle BHQ}{\sin \angle QHF}$$.
Hence we need $$\frac{BA}{AE} \cdot EH = \frac{\sin \angle BHQ}{\sin \angle QHF} \cdot BH \iff BA \cdot \sin \angle BAQ \cdot EH = AE \cdot BH \cdot \sin \angle BHQ$$Since $$\frac{BH \sin \angle BHQ}{BA \sin \angle BAQ} = \frac{BH \sin \angle BHQ}{BQ \sin \angle BQA} = \frac{\sin \angle BQH}{\sin \angle BQA} = \frac{BZ}{BA} = \frac{EH}{AE}$$we are done.
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m4thbl3nd3r
276 posts
#4
Y by
A solution without any antipode or MMP (because I haven't knew those :blush:)
Sketch
Let $AR$ be diameter of $(ABC)$, $N$ be midpoint of $EF$, $I$ be foot of perpendicular line from $M$ to $BF$. Thus, it remains to prove that $K,N,T$ is collinear, but it is easily proven that $K,M,R$ is collinear and $MN\parallel AO$ (Because $MN\perp EF,EF\perp AO$). Thus, it suffices to prove that $\frac{MN}{TR}=\frac{KM}{KR}$. But notice that $\frac{KM}{KR}=\frac{KI}{KB}=\frac{NI}{BT}$ and $\triangle NIM \sim \triangle TBR$. Thus, $\frac{KM}{KR}=\frac{KI}{KB}=\frac{NI}{BT}=\frac{MN}{TR}$ and we're done
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hanzo.ei
19 posts
#5
Y by
MathLuis wrote:
You can actually MMP this twice and since its late I'll only give a sketch.
Let $A'$ antipode of $A$ on $\triangle ABC$ then $H,M,A'$ can be easly MMP'd as $H,M$ boh have degree one by simply checking where your cases are $F=B, E=C, E=F=A$ and $H$ orthocenter. Now from this notice $K$ also has degree one snd so does $T$ now which means that $K,N,T$ colinear is degree 4 and the cases are $E=A, E=C, F=B$ and $H$ orthocenter of $\triangle ABC$, where on this case its just trivial by Pascal on $(AH)$ so you are done.

sorry my english is not good, so what do antipode and MMP mean?
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GreekIdiot
167 posts
#6
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Its a projective solution... Unless you are good in transformations I think you arent familiar with the terms even in your native language.
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maths_enthusiast_0001
133 posts
#7 • 1 Y
Y by hanzo.ei
hanzo.ei wrote:
sorry my english is not good, so what do antipode and MMP mean?
Antipode is diametrically opposite point and MMP is method of moving points.
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