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Plane Geometry is about flat shapes like lines, circles and triangles , shapes that can be drawn on a piece of paper

3 votes
2 answers
362 views

Equal area of sum of pair opposite polygons conjecture

I am looking for a proof that: if $A_{11}A_{12}...A_{1n}$; $A_{21}A_{22}...A_{2n}$; $\cdots$; $A_{i1}A_{i2}...A_{in}$; $\cdots$; $A_{m1}A_{m2}...A_{mn}$ are $m$ oriented regular polygons ($n$-gons), w …
Đào Thanh Oai's user avatar
6 votes
1 answer
365 views

Like Bradley’s conjecture (Four incenters lie on a circle) [closed]

Please don't close this question. Because there is simple configuration with 57 vote up, and don't close. Why you vote up that question and You vote to close this question? A problem I posed at here …
Đào Thanh Oai's user avatar
1 vote
0 answers
172 views

Four incenters lie on a circle-Does this theorem have a name?

When I read the new paper 100 CHARACTERIZATIONS OF TANGENTIAL QUADRILATERALS-section 7, I remember that I posed some problem associated with tangential quadrilateral from 2014 in here and 2015 in here …
Đào Thanh Oai's user avatar
1 vote
0 answers
92 views

A special configuration of Nine Circles Theorem and Eight Circle Theorem

The result as follows from special configuration of merge Nine Circle Theorem and Eight Circle theorem but it is new: Problem: Let three circle $(A)$, $(B)$, $(C)$ , let $A_c$ be arbitrary point in th …
Đào Thanh Oai's user avatar
9 votes
1 answer
1k views

Possible new theorem in plane geometry encompassing 5 famous geometry theorems

I am looking for a proof of a generalization Napoleon theorem, Bottema theorem and Brahmagupta theorem and van Aubel theorem, and Finsler–Hadwiger theorem in one configuration, as follows: Let four po …
Đào Thanh Oai's user avatar
2 votes

Dao's theorem on six circumcenters associated with a cyclic hexagon

The solution of problem in our paper On an Extension of Miquel's Theorem to a Cyclic Hexagon; Relative configuration in here On the eight circles theorem and its dual
Đào Thanh Oai's user avatar
18 votes
3 answers
1k views

An ellipse through 12 points related to Golden ratio

I am looking for a proof of the problem as follows: Let $ABC$ be a triangle, let points $D$, $E$ be chosen on $BC$, points $F$, $G$ be chosen on $CA$, points $H$, $I$ be chosen on $AB$, such that $IF$ …
Đào Thanh Oai's user avatar
0 votes
0 answers
166 views

Infinity new equilateral triangles in one configuration of triangle plane

An equilateral triangle constructed from a reference triangle is a topic which is intersested by plane geometry lovers. See Napoleon equilateral triangle, Morley equilateral triangle....In this topic …
Đào Thanh Oai's user avatar
2 votes
1 answer
367 views

What is the symmetry group of this configuration?

This configuration appear as problem 3845 in Crux Mathematicorum. I see it is very beautiful. This configuration are generalization of Pascal theorem and Brianchon theorem: Consider six points $A_1$, …
Đào Thanh Oai's user avatar
5 votes
1 answer
357 views

Discovered 240 new circles associated with Pascal's line

I am looking for a proof or a reference request for a problem as follows: Problem: Let a cyclic hexagon with sidelines $l_1$, $l_2$, $l_3$, $l_4$, $l_5$, $l_6$ and $l_1 \cap l_4 =A$, $l_3 \cap l_6 = …
Đào Thanh Oai's user avatar
3 votes
0 answers
298 views

A problem on configuration of Dao's theorem on six circumcenters

Abstract: In the figure belows: Three lines through center of pair opposite red circle are concurrent. This is a statement of Dao's theorem on six circumcenter, a new theorem in plane geometry which w …
Đào Thanh Oai's user avatar
2 votes
0 answers
211 views

A generalization of the Archimedean circle

I proposed a generalization of the Archimedean circle : In this figure $M$ is the midpoint of $AB$, $DE$; $(G)$, $(H)$, $(M)$ are the semicircles. Then two yellow circles are congruent. Question: Is t …
Đào Thanh Oai's user avatar
1 vote
0 answers
111 views

Is the formula known? and can we generalized for higher dimensions?

In this configuration as follows, we have a nice formula: $$\cos(\varphi)=\frac{OF.OE+OB.OC}{OF.OB+OE.OC}$$ Is the formula known? and can we generalized for higher dimensions?
Đào Thanh Oai's user avatar
3 votes
1 answer
417 views

Generalization of some plane geometry theorems

Conjecture: Let $A_1, A_2,\dotsc,A_n$; $B_1, B_2,\dotsc,B_n$ and $C_1, C_2,\dotsc,C_n$ be $3n$ points in the plane such that $\angle{\overrightarrow{A_iB_i}, \overrightarrow{A_{i+1}B_{i+1}}}=\frac{2 …
Đào Thanh Oai's user avatar
3 votes
1 answer
403 views

Generalization of Tucker circle, Conway circle and van Lamoen circle

Theorem 9.1 in this paper as follows is a generalization of Turker circle. Turker circles is a generalization of many circles as: Cosine Circle, circum circle, First Lemoine Circle, Gallatly Circle, K …
Đào Thanh Oai's user avatar

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