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9 Isogonal and isotomic conjugates
V0305   13
N 2 hours ago by ohiorizzler1434
1. Do you think isogonal conjugates should be renamed to angular conjugates?
2. Do you think isotomic conjugates should be renamed to cevian conjugates?

Please answer truthfully :)

Credit to Stead for this renaming idea
13 replies
V0305
May 26, 2025
ohiorizzler1434
2 hours ago
Prove atleast one from a,b,c is 2
Darealzolt   2
N 3 hours ago by sqing
Let \(a,b,c\) be real numbers, such that
\[
a^2+b^2+c^2+abc=5
\]\[
a+b+c=3
\]Prove that atleast one of the numbers \(a,b,c\) is equal to \( 2\).
2 replies
Darealzolt
Yesterday at 11:31 AM
sqing
3 hours ago
Interesting Geometry
captainmath99   4
N Yesterday at 8:01 PM by captainmath99
Let ABC be a right triangle such that $\angle{C}=90^\circ, CA=6, CB=4$. A circle O with center C has a radius of 2. Let P be a point on the circle O.

a)What is the minimum value of $(AP+\dfrac{1}{2}BP)$?
Answer Check

b) What is the minimum value of $(\dfrac{1}{3}AP+BP)$?
Answer Check
4 replies
captainmath99
May 25, 2025
captainmath99
Yesterday at 8:01 PM
Looking for even one person to study math.
abduqahhor_math   2
N Yesterday at 6:25 PM by EaZ_Shadow
Hi guys,I am looking for a person to study math topics related to olympiad.I have just finished 10th grade
2 replies
abduqahhor_math
Yesterday at 5:22 PM
EaZ_Shadow
Yesterday at 6:25 PM
Great Geometry with Squares on sides of triangles
SomeonecoolLovesMaths   3
N Yesterday at 6:14 PM by sunken rock
Three squares are drawn on the sides of triangle \(ABC\) (i.e., the square on \(AB\) has \(AB\) as one of its sides and lies outside \(ABC\)). Show that the lines drawn from the vertices \(A\), \(B\), and \(C\) to the centers of the opposite squares are concurrent.

IMAGE
3 replies
SomeonecoolLovesMaths
May 22, 2025
sunken rock
Yesterday at 6:14 PM
rare creative geo problem spotted in the wild
abbominable_sn0wman   0
Yesterday at 6:04 PM
The following is the construction of the twindragon fractal.

Let $I_0$ be the solid square region with vertices at
\[
(0, 0), \left(\frac{1}{2}, \frac{1}{2}\right), (1, 0), \left(\frac{1}{2}, -\frac{1}{2}\right).
\]
Recursively, the region $I_{n+1}$ consists of two copies of $I_n$: one copy which is rotated $45^\circ$ counterclockwise around the origin and scaled by a factor of $\frac{1}{\sqrt{2}}$, and another copy which is also rotated $45^\circ$ counterclockwise around the origin and scaled by a factor of $\frac{1}{\sqrt{2}}$, and then translated by $\left(\frac{1}{2}, -\frac{1}{2}\right)$.

We have displayed $I_0$ and $I_1$ below.

Let $I_\infty$ be the limiting region of the sequence $I_0, I_1, \dots$.

The area of the smallest convex polygon which encloses $I_\infty$ can be written as $\frac{a}{b}$ for relatively prime positive integers $a$ and $b$. Find $a + b$.
0 replies
abbominable_sn0wman
Yesterday at 6:04 PM
0 replies
Inequalities
lgx57   0
Yesterday at 3:55 PM
Let $a,b,c,d,e \ge 0$,$\sum \dfrac{1}{a+4}=1$.Prove that:
$$\sum \dfrac{a}{a^2+4} \le 1$$
Let $x,y,z>0$.Prove that:
$$\sum (y+z)\sqrt{\dfrac{yz}{(z+x)(y+x)}} \ge x+y+z$$
0 replies
lgx57
Yesterday at 3:55 PM
0 replies
Find the number of ordered triples (p,q,r)
Darealzolt   2
N Yesterday at 2:25 PM by elizhang101412
Let \(p,q,r\) be prime numbers such that
\[
\frac{1}{pq}+\frac{1}{qr}+\frac{1}{pr}=\frac{1}{839}
\]Hence find the numbers of ordered triples \(\{p,q,r\}\)
2 replies
Darealzolt
Yesterday at 1:52 PM
elizhang101412
Yesterday at 2:25 PM
Find the sum of all the products a_i a_j
Darealzolt   1
N Yesterday at 2:13 PM by alexheinis
Among the 100 constants \( \{ a_1,a_2,a_3,\dots,a_{100} \} \),there are \(39\) equal to \( -1\), and \(61\) equal to \(1\). Find the sum of all the products \(a_i a_j\) , where \(a \leq i < j \leq 100\).
1 reply
Darealzolt
Yesterday at 11:24 AM
alexheinis
Yesterday at 2:13 PM
IOQM P26 2024
SomeonecoolLovesMaths   5
N Yesterday at 1:11 PM by SomeonecoolLovesMaths
The sum of $\lfloor x \rfloor$ for all real numbers $x$ satisfying the equation $16 + 15x + 15x^2 = \lfloor x \rfloor ^3$ is:
5 replies
SomeonecoolLovesMaths
Sep 8, 2024
SomeonecoolLovesMaths
Yesterday at 1:11 PM
Projective training on circumscribds
Assassino9931   1
N Apr 10, 2025 by VicKmath7
Source: Bulgaria Balkan MO TST 2025
Let $ABCD$ be a circumscribed quadrilateral with incircle $k$ and no two opposite angles equal. Let $P$ be an arbitrary point on the diagonal $BD$, which is inside $k$. The segments $AP$ and $CP$ intersect $k$ at $K$ and $L$. The tangents to $k$ at $K$ and $L$ intersect at $S$. Prove that $S$ lies on the line $BD$.
1 reply
Assassino9931
Apr 9, 2025
VicKmath7
Apr 10, 2025
Projective training on circumscribds
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Source: Bulgaria Balkan MO TST 2025
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Assassino9931
1379 posts
#1
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Let $ABCD$ be a circumscribed quadrilateral with incircle $k$ and no two opposite angles equal. Let $P$ be an arbitrary point on the diagonal $BD$, which is inside $k$. The segments $AP$ and $CP$ intersect $k$ at $K$ and $L$. The tangents to $k$ at $K$ and $L$ intersect at $S$. Prove that $S$ lies on the line $BD$.
This post has been edited 1 time. Last edited by Assassino9931, Apr 9, 2025, 10:36 PM
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VicKmath7
1391 posts
#2
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Let $k$ touch $AB, BC, CD, DA$ at $T_a, T_b, T_c, T_d$ and let $T_aT_b \cap T_cT_d=X$. Since $B$ is the pole of $T_aT_b$ and $D$ is the pole $T_cT_d$, $X$ is the pole of $BD$. By Pascal $X, A, C$ and $T_aT_c \cap T_bT_d$ are collinear. Let $BD\cap k=E, F$ and $AC \cap BD=T$; we have to show that $KELF$ is harmonic, and since $XE, XF$ touch $k$, we have to show $X \in KL$. Moreover, $(AC; TX)=-1$ by projecting $(T_aT_b;RX)=-1$ through $B$ onto $AC$, where $R=T_aT_b \cap BD$.

Now that we have done the known stuff, we can finish easily. Redefine $K, L\in k$ such that the line $KL$ passes through $X$ and we will show that $AK, CL$ concur on $BD$. Indeed, if $KL \cap BD=T'$, then $(KL;T'X)=(AC;TX)=-1$, so prism lemma implies that $AK, CL, TT'$ concur, as desired.
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