ETC

X(68177) = EULER LINE INTERCEPT OF X(76)X(3793)

Barycentrics    -6 a^4+a^2 (b^2+c^2)+b^4-6 b^2 c^2+c^4 : :

As a point on the Euler line, X(68177) has Shinagawa coefficients: {2 (E+F)^2-3 S^2,7 S^2}

See Juan José Isach Mayo, euclid 8245.

X(68177) lies on these lines: {2, 3}, {32, 63923}, {76, 3793}, {698, 5052}, {736, 15480}, {1506, 32459}, {1975, 18907}, {3053, 64093}, {3589, 7756}, {3734, 7767}, {3788, 53418}, {3933, 7737}, {3972, 5305}, {5034, 42421}, {5215, 12815}, {5475, 59545}, {5503, 60146}, {5943, 58211}, {6337, 15484}, {6390, 7745}, {6392, 21309}, {6645, 15172}, {6680, 53419}, {7747, 7789}, {7753, 59546}, {7760, 52229}, {7768, 63945}, {7783, 53489}, {7784, 43618}, {7787, 63633}, {7794, 63941}, {7804, 63548}, {7812, 32820}, {7839, 47287}, {7858, 59634}, {7863, 14537}, {15491, 15515}, {15513, 58446}, {17130, 63928}, {18501, 39141}, {18844, 60262}, {19661, 34505}, {22253, 32822}, {22331, 63955}, {30103, 65632}, {30104, 65631}, {30435, 32815}, {31664, 31665}, {32520, 61624}, {32836, 63936}, {39590, 44377}, {40894, 40895}, {53106, 60186}, {60209, 62912}

X(68177) = midpoint of X(i) and X(j) for these {i,j}: {384, 19687}, {6656, 6658}, {6661, 66328}, {19686, 66319}, {19695, 19696}
X(68177) = reflection of X(i) in X(j) for these {i,j}: {6655, 8364}, {6656, 19697}, {7819, 384}, {8357, 7819}, {19695, 66347}, {66318, 66321}, {66321, 66319}, {66326, 66318}, {66335, 6661}, {66349, 66340}
X(68177) = complement of X(19695)
X(68177) = anticomplement of X(66347)
X(68177) = {X(i),X(j)}-harmonic conjugate of X(k) for these (i,j,k): {2, 19695, 66347}, {2, 19696, 19695}, {2, 33250, 548}, {3, 32981, 66391}, {4, 8361, 37350}, {4, 8369, 8361}, {4, 33181, 11318}, {4, 33201, 32954}, {5, 14035, 66409}, {20, 8362, 8354}, {20, 11286, 8362}, {140, 3552, 27088}, {382, 14001, 33184}, {384, 6655, 6661}, {384, 6656, 19697}, {384, 6658, 6656}, {384, 7819, 66318}, {384, 7924, 19692}, {384, 7948, 66317}, {384, 19686, 19687}, {384, 19688, 19677}, {384, 19691, 19702}, {384, 19693, 66319}, {384, 19696, 2}, {384, 33256, 19689}, {384, 66328, 6655}, {439, 32983, 3526}, {546, 66393, 7807}, {550, 7770, 8359}, {1003, 14035, 5}, {1656, 32979, 3363}, {3146, 7866, 66392}, {3146, 14039, 7866}, {3529, 33198, 11287}, {3530, 66412, 32992}, {3552, 8370, 140}, {3552, 14034, 8370}, {3830, 33242, 14064}, {3853, 8368, 5025},{3972, 32819, 5305}, {5025, 66408, 3853}, {5059, 32956, 5077}, {5073, 33237, 32974}, {6655, 6661, 8364}, {6655, 8364, 66335}, {6655, 19694, 6656}, {6655, 66320, 384}, {6655, 66335, 8357}, {6656, 6661, 19694}, {6656, 7819, 66343}, {6656, 19687, 6658}, {6656, 19689, 66344}, {6656, 19694, 8364}, {6656, 19697, 7819}, {6656, 66343, 66326}, {6658, 19689, 33256}, {6661, 8364, 7819}, {6661, 66319, 66320}, {7439, 21490, 19280},{7745, 7816, 6390}, {7770, 33007, 550}, {7791, 66387, 15704}, {7807, 11361, 546}, {7819, 8357, 66326}, {7819, 66321, 384}, {7819, 66335, 8364}, {7824, 8598, 33923}, {7841, 14037, 33185}, {7841, 33280, 62036}, {7887, 14068, 3845}, {7892, 33229, 8360}, {7892, 66419, 33229}, {7924, 19692, 66342}, {7924, 66342, 66346}, {7948, 19691, 66349}, {7948, 19702, 66340}, {7948, 66317, 19702}, {8356, 33257, 12103}, {8357, 66318, 7819}, {8357, 66343, 6656}, {8358, 62123, 33260}, {8360, 62026, 33229}, {8363, 33019, 66394}, {8363, 66423, 33019}, {8366, 33283, 33212}, {8367, 33923, 7824}, {11285, 33244, 8703}, {11317, 32961, 3858}, {13586, 32992, 3530}, {14031, 33007, 7770}, {14033, 32981, 3}, {14033, 33239, 32971}, {14033, 66391, 66415}, {14036, 33019, 8363}, {14036, 66423, 66394}, {14037, 33280, 7841}, {14038, 66405, 7933}, {14042, 33225, 33228}, {14042, 33228, 3861}, {14063, 33220, 33186}, {14068, 33255, 7887}, {15687, 33186, 14063}, {16044, 35297, 3628}, {16898, 33193, 33234}, {16924, 33187, 33235}, {16924, 33235, 549}, {16925, 33016, 33270}, {16925, 33270, 33233}, {19670, 66320, 19696}, {19686, 19693, 384}, {19686, 66320, 66328}, {19687, 66319, 384}, {19687, 66320, 8364}, {19687, 66321, 8357}, {19689, 33256, 6656}, {19689, 66344, 7819}, {19690, 66322, 66341}, {19690, 66341, 66334}, {19691, 66317, 7948}, {19692, 66346, 7819}, {19697, 66344, 19689}, {19702, 66340, 7819}, {19702, 66349, 7948}, {32954, 33201, 8369}, {32964, 44543, 632}, {32968, 35927, 3}, {32971, 32981, 33239}, {32971, 33239, 3}, {32975, 35287, 15720}, {32979, 32985, 1656}, {32991, 33216, 5070}, {32997, 66395, 62159}, {33016, 33233, 5}, {33018, 33246, 33249}, {33018, 33249, 5066}, {33019, 66423, 62034}, {33183, 50687, 33292}, {33185, 62036, 7841}, {33193, 33234, 62155}, {33214, 35955, 550}, {33229, 35954, 7892}, {33229, 66419, 62026}, {35954, 66419, 8360}, {37060, 38071, 32963}, {62034, 66394, 33019}, {66317, 66349, 66340}, {66320, 66328, 6661}

---

JOHN H. CONWAY Papers

Bibliography of John H. Conway.

ARTICLES AND PAPERS

M.R. Boothroyd and John H. Conway, Problems Drive, 1959. Eureka 22 (October 1959) 15-17. (Solutions: 22-23).
EUREKA

John H. Conway and M.J.T. Guy, Π in four 4’s. Eureka 25 (October 1962) 18-19.
EUREKA

John H. Conway, Tomorrow is the Day After Doomsday. Eureka 36 (October 1973) 28-31.
EUREKA

John H. Conway, The Hunting of J4. Eureka 41 (Summer 1981), 46-54.
EUREKA

John H. Conway, The Weird and Wonderful Chemistry of Audioactive Decay. Eureka 46 (January 1986) 5-18.
EUREKA

John H. Conway, Forewod. In: G. Polya, How to solve it. A new aspect of mathematical method. Expanded version of the 1988 edition, with a new foreword by John H. Conway. Princeton Science Library. Princeton University Press, Princeton, NJ, 2004, p. xix-xxiv.
POLYA

John Conway, The Power of Mathematics. In: Alan Blackwell and David MacKay (Editors), Power (Darwin College Lectures, Series Number 16). Cambridge University Press 2006, pp 36-50
John Conway

Conway J, Ryba A. The Steiner-Lehmus angle-bisector theorem. The Mathematical Gazette. 2014;98(542):193-203. doi:10.1017/S0025557200001236
Conway-Ryba-Lehmus

Buchanan, A.G., Conway, J.H. (2017). An Island Tale for Young Anthropologists. In: Fitting, M., Rayman, B. (eds) Raymond Smullyan on Self Reference. Outstanding Contributions to Logic, vol 14. Springer, Cham. https://doi.org/10.1007/978-3-319-68732-2_10
Buchanan-Conway

Douglas Hofstadter, FOREWORD

Douglas Hofstadter, FOREWORD
In: Clark Kimberling, Triangle Centers and Central Triangles. Congressus Numerantum, vol. 129, August, 1998. Winnipeg, Canada

Douglas Hofstadter

REGULAR POLYGONS AND EULER LINES

Let A1A2A3 be an equilateral triangle and Pa point.
Denote:
1, 2, 3 = the Euler lines of PA1A2,PA2A3, PA3A1, resp.
1,2,3 are concurrent.
Hyacinthos 21592

GENERALIZATION
Let A1A2A3...A3k be a regular 3k-gon and P a point.
Denote:
1, 2, 3,.... 3k = the Euler lines of PA1A2, PA2A3, PA3A4,.....PA3kA1, resp.
These triads are concurrent
1, k+1, 2k+1
2, k+2, 2k+2
3, k+3, 2k+3
4, k+4, 2k+4
......
k, 2k, 3k

k = 2 (Regular Hexagon)
1, 3, 5
2, 4, 6

Mail Antreas P. Hatzipolakis

X(5159) updated

X(5159) = INVERSE-IN-NINE-POINT-CIRCLE OF X(1368)

Barycentrics   f(a,b,c) : f(b,c,a) : f(c,a,b), where f(a,b,c) = (b² + c² - a²)(3b⁴ + 3c⁴ - 2a⁴ + a²b² + a²c² - 6b²c²)
Barycentrics    (a^2-b^2-c^2)*(2*a^4-3*(b^2-c^2)^2-a^2*(b^2+c^2)) : :
Barycentrics    SA*(6*SB*SC-SB*SW-SC*SW) : :
X(5159) = 9*X(2)-X(23), 3*X(2)+X(858), 5*X(2)-X(7426), 7*X(2)+X(10989), 3*X(2)+5*X(30745), 6*X(2)-X(37897), 7*X(2)-X(37904), 11*X(2)-3*X(37907), 9*X(2)+X(46517), 5*X(2)+X(47311), 11*X(2)-X(47312), 6*X(2)+X(47315), 9*X(2)-2*X(47316), 3*X(2)+2*X(47629), X(3)+3*X(2072), X(3)-3*X(10257), 2*X(3)-3*X(16976), 3*X(3)+X(18323), 5*X(3)+3*X(18403), 7*X(3)-3*X(44246)

As a point on the Euler line, X(5159) has Shinagawa coefficients (E -5*F, -E - F)

X(5159) = (inverse-in-de-Longchamps-circle of X(22)) = (radical trace of nine-point circle and de-Longchamps circle) = (radical trace of polar circle and de-Longchamps circle) = (reflection of X(23) in de Longchamps line)    (Randy Hutson, August-September, 2013)

For a construction of X(5159), see David Nguyen and Ercole Suppa, euclid 7508.

X(5159) lies on these lines: {1, 47489}, {2, 3}, {6, 47546}, {8, 47533}, {10, 47492}, {39, 47182}, {69, 40920}, {98, 44877}, {114, 16177}, {122, 16188}, {125, 3292}, {126, 38971}, {127, 31655}, {131, 46436}, {141, 8542}, {193, 47463}, {216, 3055}, {230, 3284}, {265, 55981}, {325, 16315}, {339,3266}, {343, 8538}, {373, 37511}, {385, 47237}, {394, 8548}, {511, 6723}, {523, 4885}, {524, 6698}, {525, 22264}, {551, 47491}, {575, 23292}, {576, 13567}, {577, 3054}, {597, 47460}, {599, 47280}, {625,40544}, {647, 47256}, {850, 47248}, {892, 16103}, {895, 15128}, {1007, 2452}, {1038, 7286}, {1040, 5160}, {1092, 61544}, {1125, 51725}, {1154, 64689}, {1351, 37643}, {1352, 59767}, {1353, 26869}, {1503, 5972}, {1514, 36518}, {1531, 38727}, {1560, 52951}, {1568, 38729} ,{1698, 47321}, {1853, 59543}, {1899, 38398}, {1992, 47462}, {2697, 44060}, {2770, 58096}, {3066, 38136}, {3167, 23291}, {3231, 14965}, {3241, 47536}, {3258, 31842}, {3291, 14961}, {3576, 47469}, {3580, 15059}, {3589, 20113}, {3618, 32220}, {3619, 47279}, {3620, 47281}, {3634, 37613}, {3679, 47490}, {3763, 32113}, {3815, 5158}, {3818, 61507}, {4669, 47564}, {5093, 63081}, {5099, 31275}, {5203, 53895}, {5272, 10149}, {5297, 18447}, {5622, 41615}, {5650, 9967}, {5651, 18358}, {5886, 47471}, {6000, 65095}, {6390, 15398}, {6425, 18289}, {6426, 18290}, {6509, 15850}, {6593, 15116}, {6688, 58481}, {6697, 13562}, {6721, 62490}, {6776, 62708}, {7292, 18455}, {7736, 47184}, {7745, 15820}, {7763, 59766}, {7868, 16325}, {7925, 47155}, {7998, 18438}, {8263, 23327}, {8280, 43879}, {8281, 43880}, {8705, 11574}, {8780, 32064}, {8854, 53513}, {8855, 53516}, {9019, 35370}, {9140, 32272}, {9148, 47159}, {9165, 44401}, {9300, 15860}, {9306, 23332}, {9716, 45968}, {9745, 63633}, {9771, 16333}, {9775, 46637}, {9820, 18914}, {9970, 15131}, {10116, 15129},{10173, 11594}, {10192, 64196}, {10256, 46987}, {10415, 34897}, {10510, 47558}, {10516, 47474}, {10564, 23515}, {10634, 43103}, {10635, 43102}, {11059, 41009}, {11245, 11422}, {11427, 53092}, {11433, 11482}, {11477, 26958}, {11513, 32789}, {11514, 32790}, {11580, 22121}, {12041, 58885}, {12079, 14919}, {12358, 40685}, {12900, 14915}, {13202, 20725}, {13292, 15120}, {13445, 15029}, {13561, 31831}, {13611, 65620}, {13754, 16270}, {13857, 41586}, {13869, 30741}, {14156, 15115}, {14341, 41357}, {14389, 51732}, {14561, 47571}, {14984, 60774}, {15025, 50435}, {15027, 22115}, {15034, 25739}, {15066, 61545}, {15124, 50708}, {15125, 15311}, {15139, 15142}, {15448, 29012}, {15471, 32300}, {15491, 16324}, {15526, 22110}, {15533, 47466}, {15812, 47355}, {15819, 47568}, {15905, 62992}, {16092, 39061}, {16227, 64854}, {16303, 31489}, {16310, 44529}, {16313, 50666}, {16760, 34844}, {18583, 37648}, {18911, 61690}, {19126, 32217}, {19131, 22112}, {19862, 51693}, {19875, 47488}, {19883, 47495}, {20190, 58447}, {20208, 37690}, {20299, 59659}, {20582, 47446}, {21243, 53415}, {21356, 47551}, {21358, 47276}, {21639, 53778}, {21850, 61506}, {21968, 64059}, {21970, 51212}, {22104, 34841}, {22151, 32251}, {23878, 47247}, {25055, 47472}, {29181, 32223}, {29639, 47178}, {31174, 46983}, {31274, 47326}, {31277, 47004}, {31279, 47173}, {31804, 64181}, {31843, 46664}, {32111, 64101}, {32227, 34153}, {32269, 51360}, {32411, 63709}, {32767, 64035}, {33522, 55602}, {33924, 47164}, {34128, 51391}, {34988, 44533}, {35259, 39884}, {35707, 58437}, {35968, 42426}, {36900, 47257}, {37638,48876}, {37644, 61624}, {37647, 62698}, {37688, 41008}, {37689, 38292}, {38028, 47476}, {38047, 47506}, {38053, 47507}, {38057, 47508}, {38098, 47534}, {38110, 54012}, {38314, 47493}, {38317, 47581}, {38795, 51425}, {39220, 52058}, {39899, 64177}, {40112, 41724}, {40341, 47465}, {40349, 40350}, {40995, 63098}, {41139, 46998}, {42424, 53832}, {44381, 47239}, {44436, 47213}, {46264, 61680}, {46686, 58871}, {46982, 63440}, {46986, 47245}, {46989, 47254}, {47169, 62196}, {47175, 47259}, {47207, 65760}, {47249, 47261}, {47253, 47442}, {47271 ,54320}, {47352, 47458}, {47447, 63121}, {47451, 51128}, {47456, 52238}, {47461, 51171}, {47494, 53620}, {47499, 47761}, {47500, 47760}, {47537, 51071}, {47541, 59373}, {47544, 48310}, {47575, 59403}, {47576, 59404}, {51358, 59661}, {52520, 63632}, {52987, 61646}, {53777, 62375}, {58451, 58639}, {59399, 63084}, {60414, 60415}, {60420, 60424}, {60421, 60425}, {60422, 60426}, {60423, 60427}

X(5159) = midpoint of X(i) and X(j) for these (i, j): {2, 47097}, {3, 10297}, {5, 15122}, {23, 46517}, {69, 47277}, {125, 11064}, {325, 16315}, {403, 47090}, {427, 16387}, {441, 37987}, {468, 858}, {625, 40544}, {850, 47248}, {892, 16103}, {1529, 46620}, {2071, 10151}, {2072, 10257}, {3153, 37931}, {3679, 47593}, {5189, 37899}, {5196, 47098}, {5203, 53895}, {6390, 51258}, {7426, 47311}, {7575, 47341}, {9148, 47159}, {10295, 47339}, {10510, 47558}, {10989, 37904}, {12041, 58885}, {13202, 20725}, {13473, 16386}, {13857, 44569}, {15115, 15123}, {15118, 19510}, {16188, 47570}, {18323, 47308}, {18572, 47335}, {22110, 46980}, {23323, 34152}, {31174, 46983}, {32269, 51360}, {36170, 56370}, {37897, 47315}, {37900, 47095}, {37911, 47629}, {37938, 44452}, {37950, 47336}, {38971, 54075}, {46686, 58871}, {46982, 63440}, {47091, 47096}, {47092, 62344}, {47280, 47552}, {47310, 54995}, {47312, 47314}, {47612, 47613}
X(5159) = reflection of X(i) in X(j) for these (i, j): (4, 63821), (23, 47316), (403, 44912), (468, 37911), (858, 47629), (10257, 63860), (15471, 32300), (16976, 10257), (32217, 47454), (37897, 468), (37899, 47630), (37910, 37897), (37935, 44452), (37942, 44911), (37984, 5), (41357, 14341), (47004, 47262), (47114, 16976), (47239, 44381), (47261, 47249), (47296, 6723), (47315, 858), (47338, 11799), (47442, 47253), (47457, 3589), (47549, 47460), (51725, 1125), (65154, 6677)
X(5159) = complement of X(468)
X(5159) = inverse-in-nine-point circle of X(1368)
X(5159) = inverse-in-{circumcircle, nine-point circle}-inverter of X(20)
X(5159) = inverse-in-complement-of-polar-circle of X(2)
X(5159) = intersection, other than A, B, C, of circumconics {A, B, C, X(3), X(40349)} and {A, B, C, X(4), X(53419)}
X(5159) = barycentric product X(i)*X(j) for these (i,j): (69, 53419), (76, 21639), (264, 40349), (305, 40350), (525, 53351), (5485, 53778)
X(5159) = barycentric quotient X(i)/X(j) for these {i,j}: {40349, 3}, {40350, 25}, {53351, 648}, {53419, 4}, {53778, 1992}
X(5159) = trilinear product X(i)*X(j) for these (i,j): (63, 53419), (75, 21639), (92, 40349), (304, 40350), (656, 53351), (53778, 55923)
X(5159) = trilinear quotient X(i)/X(j) for these (i,j): (21639, 31), (40349, 48), (40350, 1973), (53351, 162), (53419, 19), (53778, 36277)
X(5159) = (X(i), X(j))-harmonic conjugate of X(k) for these (i, j, k): (2, 20, 52290), (2, 22, 52297), (2, 427, 6677), (2, 468, 37911), (23, 468, 47316), (597, 47549, 47460), (599, 47280, 47552), (3291, 47298, 43291), (3618, 32220, 47459), (5651, 45303, 18358), (10510, 62376, 47558), (24855, 47298, 3291), (26869, 37645, 1353), (30786, 37804, 62310), (37648, 61743, 18583), (37804, 62310, 6390), (51360, 61691, 32269), (59767, 61735, 1352)

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PYTHAGOREAN THEOREM

From a New Criterion of a Cyclic Quadrilateral (NCCQ) to Pythagorean System –– An Alternative Study
Athanasios Gakopoulos, Farsala, Greece
Debabrata Nag, Kolkata, India

Gak_Nag_Pythagoras_07-11_2024

X(370)

Created at: Sun, Nov 3, 2024 at 12:26 PM
From: Antreas Hatzipolakis
To: euclid@groups.io, Chris van Tienhoven
Subject: Re: [euclid] Homothetic to Morley

Dear Chris
1. X(5390)
The point X(5390) was listed "coordinates-less"

X(5390) = EULER-MORLEY-ZHAO POINT
Barycentrics (unknown)
Let DEF be the classical Morley triangle. The Euler lines of the three triangles AEF, BFD, CDE appear to concur in a point for which barycentric coordinates remain to be discovered.
Construction by Zhao Yong of Anhui, China, October 2, 2012.

Then you, with your fruitful "fields method", managed to find the trilinears of the point with trigonometric expressions (Hyacinthos 21902)

2. X(370)
Jiang Huanxin proposed in the American Mathematical Monthly the following problem
In triangle ABC find all points P such that the cevian triangle of P is equilateral (my wording)
The problem was solved analytically by David Goering.
(I have scanned the solution and can be found in my blog here CEVIAN TRIANGLES ) Jean-Pierre Ehrmann computed the barycentrics as unique solutions of a system of equations.

I am wondering if the trlinears of the point can be computed with trigonometric expressions, as in the point X(5390) The same for the center of the equilateral triangle in question

Greetings from sunny Athens
APH

***********************

Created at: Sun, Nov 3, 2024 at 11:48 PM
From: Chris van Tienhoven
To: Antreas Hatzipolakis
Subject: RE: Homothetic to Morley

Dear Antreas,

I am not so sure if X(370) is suitable to tackle with Perspective Fields.
In 2010 I corresponded with Francisco about X(370) and in 2012 with Peter Moses.
I had already calculated the coordinates of X(370) and I found there are 3 solutions for the specifications of X(370), two of which can be imaginary. Peter told me there even may be 6 solutions.
He wrote in 2012 to me:
There are 2 sets of 3 solutions, depending on the external Fermat (giving X(370) and a maximum of 2 imaginaries) or internal Fermat (giving 3 reals) construction.
X(370) pertains to the equilateral cevian point that is inside the triangle. Each set of solutions comes from intersecting 3 conics.
As to it being a center .. I think it probably is, but the test is to see if, when symmetrically written, the coordinates remain unchanged under a bicentric exchange. It doesn't necessarily mean that a point is not a center if the coordinates are not symmetric. It may well be possible they can be made so.
See attachment for the one real solution I found in 2012. It is pretty long.
The expression is checked with figures to be correct.
Best regards,
Chris

Chris-solution-X370-in 2012

Mail Antreas P. Hatzipolakis

CEVIAN TRIANGLES

Jiang Huanxin and David Goering, EquilateralCevian Triangles
The American Mathematical Monthly
Vol. 104, No. 6 (Jun. - Jul., 1997), pp. 567-570
David Goering
X(370) = EQUILATERAL CEVIAN TRIANGLE POINT

Mowaffaq Hajja, The Arbitrariness of the Cevian Triangle
The American Mathematical Monthly
Vol. 113, No. 5 (May, 2006), pp. 443-447
Mowaffaq Hajja

Mail Antreas P. Hatzipolakis

FEUERBACH POINT PROBLEM

Lemma 1

Let ABC be a triangle. The Oi line intersects AB at C'.The circle (Oa) with diameter AI intersects the circumcircle again at A". The line C'A" intersects (Oa) again at Ca.Ca is the orthogonal projection of A on IC.

Lemma 2

Let ABC be a triangle and Ba, Ca the orthogonal projeections of A on IB, IC, resp. The line BaCa intersects AC, AB at B'a, C'a, resp. B'a,C'a are the midpoints of AC, AB, resp.

Lemma 3

Let ABC be a triangle. Denote C' = the midpoint of AB, Ma, Mb = the midpoints of AI, BI, resp. and Ba = the orthogonal projection of A on BI. The points Ma, C', Mb, Ba are concyclic. The circle is the NPC of AIB.

Problem
By David Nguyen

Rewritten with cyclic notation
Let ABC be a triangle. The OI line intersects BC, CA, AB at A', B', C', resp.  
Denote
(Oa) = the circle with diameter AI
A" = the 2nd intersection of the circumcircle and (Oa)
Ba = the 2nd intersection of B'A" and (Oa)
Ca = the 2nd intersection of C'A" and (Oa)
B'a = BaCa ∩ AC  , C'a = BaCa ∩ AB

(Oab) = the circumcircle of OaB'aCa
(Oac)= the circumcircle of OaBaC'a
The 2nd intersection of (Oab), (Oac) is the Feuerbach point

Proof
By the lemmata, the problem is equivalent to the following problem
Let ABC be a triangle and A'B'C' the medial triangle
Denote
A", B", C" = the midpoints of IA, IB, IC, resp.
The circumcircles of A'B"C", B'C"A", C'A"B" concur at the Feuerbach point
True, since the circumcircles of A'B"C", B'C"A", C'A"B" are the NPCs of IBC ICA, IAB resp. and they concur at the Poncelet point of ABCI = the Feuerbach point.

Mail Antreas P. Hatzipolakis

PANAKIS' PSEUDOISOSCELES TRIANGLE

Let ABC be a trangle and D1, D2, D3 the feet of the internal angle bisectors [D1D2D3 = the cevian triangle of the incenter I]
Prove that the triangle D1D2D3 can be isosceles without ABC being isosceles.
Ioannis Panakis, Plane Trigonometry, vol. B, Athens (1973), p. 110 [in Greek]

I call this triangle ABC as Panakis pseudoisosceles triangle

Properties of ABC (in the same book pp. 109-111)
1. The A, D1, D2, D3 are concyclic [the cevian circle of I passes through A]
2. (a + b + c)*(-a^2 + b^2 + c^2) + abc = 0
3. a / (b + c) = b / (c + a) + c / (a + b)
4. (r1 - r) / (r1 + r) = ((r2 - r) / (r2 + r)) + ((r3 - r) / (r3 + r))
where r = the inradius and r1, r2, r3 the exradii.

PDF of the pages of the book Panakis

Mail Antreas P. Hatzipolakis

THEBAULT'S PSEUDOISOSCELES TRIANGLE

Victor Thebault published the following theorem as an exercise:

Si le cercle qui passe par les pieds des bissectrices intérieures d'un triangle est tangent à l'un des côtés, le triangle est isocèle, et réciproquement. 
(If the circle passing through the feet of the interior bisectors of a triangle is tangent to one of the sides, the triangle is isosceles, and vice versa.)

Solution by (A.M.)  [false]
Journal de mathématiques élémentaires.  
75e Annee - No 1 -  1er Octobre 1950, p. 3, #14250

Joseph Andersonn proved that the triangle is not necessarily isosceles.
CERCLE PASSANT PAR LES PIEDS DES BISSECTRICES INTÉRIEURES D'UN TRIANGLE ET TANGENT À L'UN DES CÔTÉS
par A. Monjallon. 
Journal de mathématiques élémentaires.  
75e Annee - No 20, 15 Juillet 1951, pp. 153 - 4

CERCLE PASSANT PAR LES PIEDS DES BISSECTRICES INTÉRIEURES D'UN TRIANGLE ET TANGENT À L'UN DES CÔTÉS
par Rene Blanchard. 
Journal de mathématiques élémentaires.  
76e Annee - No 4, 15 Novembre 1951, pp. 25 - 6 

PDF File Victor Thebault

Francisco Javier García Capitán's Solution (in Spanish)
wrong-thebault

Mail Antreas P. Hatzipolakis

FJGC A confluence of concepts

Francisco Javier García Capitán,A confluence of concepts
FJGC

FORUM GEOMETRICORUM

FORUM GEOMETRICORUM

All Volumes

FJGC, An unique orthocentroidal system

Euclid 6412

Francisco Javier García Capitán, An unique orthocentroidal system
FJGC

ETC APH-FJGC-EULER

X(44234) = 1ST HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

X(44898) = 2ND HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

X(45306) = 3RD HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

X(45307) = 4TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

X(45308) = 5TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

X(64480) = 6TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

Barycentrics    -a^16 b^2 + 5 a^14 b^4 - 9 a^12 b^6 + 5 a^10 b^8 + 5 a^8 b^10 - 9 a^6 b^12 + 5 a^4 b^14 - a^2 b^16 - a^16 c^2 - 2 a^14 b^2 c^2 + 3 a^12 b^4 c^2 + 13 a^10 b^6 c^2 - 23 a^8 b^8 c^2 + 13 a^6 b^10 c^2 - 6 a^4 b^12 c^2 + 4 a^2 b^14 c^2 - b^16 c^2 + 5 a^14 c^4 + 3 a^12 b^2 c^4 - 28 a^10 b^4 c^4 + 17 a^8 b^6 c^4 + 17 a^6 b^8 c^4 - 7 a^4 b^10 c^4 - 12 a^2 b^12 c^4 + 5 b^14 c^4 - 9 a^12 c^6 + 13 a^10 b^2 c^6 + 17 a^8 b^4 c^6 - 42 a^6 b^6 c^6 + 8 a^4 b^8 c^6 + 28 a^2 b^10 c^6 - 9 b^12 c^6 + 5 a^10 c^8 - 23 a^8 b^2 c^8 + 17 a^6 b^4 c^8 + 8 a^4 b^6 c^8 - 38 a^2 b^8 c^8 + 5 b^10 c^8 + 5 a^8 c^10 + 13 a^6 b^2 c^10 - 7 a^4 b^4 c^10 + 28 a^2 b^6 c^10 + 5 b^8 c^10 - 9 a^6 c^12 - 6 a^4 b^2 c^12 - 12 a^2 b^4 c^12 - 9 b^6 c^12 + 5 a^4 c^14 + 4 a^2 b^2 c^14 + 5 b^4 c^14 - a^2 c^16 - b^2 c^16 + 4 a^13 b c OH S - 6 a^11 b^3 c OH S - 6 a^9 b^5 c OH S + 10 a^7 b^7 c OH S + 6 a^5 b^9 c OH S - 12 a^3 b^11 c OH S + 4 a b^13 c OH S - 6 a^11 b c^3 OH S + 24 a^9 b^3 c^3 OH S - 12 a^7 b^5 c^3 OH S - 24 a^5 b^7 c^3 OH S + 30 a^3 b^9 c^3 OH S - 12 a b^11 c^3 OH S - 6 a^9 b c^5 OH S - 12 a^7 b^3 c^5 OH S + 36 a^5 b^5 c^5 OH S - 18 a^3 b^7 c^5 OH S + 12 a b^9 c^5 OH S + 10 a^7 b c^7 OH S - 24 a^5 b^3 c^7 OH S - 18 a^3 b^5 c^7 OH S - 8 a b^7 c^7 OH S + 6 a^5 b c^9 OH S + 30 a^3 b^3 c^9 OH S + 12 a b^5 c^9 OH S - 12 a^3 b c^11 OH S - 12 a b^3 c^11 OH S + 4 a b c^13 OH S : :

See Antreas Hatzipolakis and Francisco Javier García Capitán, euclid 6388.

X(64480) lies on these lines: {2, 3), {542, 44123}, {1989, 8106}, {8115, 45016}, {13415, 18374}, {15360, 24650}, {32225, 44125}

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X(64481) = 7TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

Barycentrics    -a^16 b^2 + 5 a^14 b^4 - 9 a^12 b^6 + 5 a^10 b^8 + 5 a^8 b^10 - 9 a^6 b^12 + 5 a^4 b^14 - a^2 b^16 - a^16 c^2 - 2 a^14 b^2 c^2 + 3 a^12 b^4 c^2 + 13 a^10 b^6 c^2 - 23 a^8 b^8 c^2 + 13 a^6 b^10 c^2 - 6 a^4 b^12 c^2 + 4 a^2 b^14 c^2 - b^16 c^2 + 5 a^14 c^4 + 3 a^12 b^2 c^4 - 28 a^10 b^4 c^4 + 17 a^8 b^6 c^4 + 17 a^6 b^8 c^4 - 7 a^4 b^10 c^4 - 12 a^2 b^12 c^4 + 5 b^14 c^4 - 9 a^12 c^6 + 13 a^10 b^2 c^6 + 17 a^8 b^4 c^6 - 42 a^6 b^6 c^6 + 8 a^4 b^8 c^6 + 28 a^2 b^10 c^6 - 9 b^12 c^6 + 5 a^10 c^8 - 23 a^8 b^2 c^8 + 17 a^6 b^4 c^8 + 8 a^4 b^6 c^8 - 38 a^2 b^8 c^8 + 5 b^10 c^8 + 5 a^8 c^10 + 13 a^6 b^2 c^10 - 7 a^4 b^4 c^10 + 28 a^2 b^6 c^10 + 5 b^8 c^10 - 9 a^6 c^12 - 6 a^4 b^2 c^12 - 12 a^2 b^4 c^12 - 9 b^6 c^12 + 5 a^4 c^14 + 4 a^2 b^2 c^14 + 5 b^4 c^14 - a^2 c^16 - b^2 c^16 - 4 a^13 b c OH S + 6 a^11 b^3 c OH S + 6 a^9 b^5 c OH S - 10 a^7 b^7 c OH S - 6 a^5 b^9 c OH S + 12 a^3 b^11 c OH S - 4 a b^13 c OH S + 6 a^11 b c^3 OH S - 24 a^9 b^3 c^3 OH S + 12 a^7 b^5 c^3 OH S + 24 a^5 b^7 c^3 OH S - 30 a^3 b^9 c^3 OH S + 12 a b^11 c^3 OH S + 6 a^9 b c^5 OH S + 12 a^7 b^3 c^5 OH S - 36 a^5 b^5 c^5 OH S + 18 a^3 b^7 c^5 OH S - 12 a b^9 c^5 OH S - 10 a^7 b c^7 OH S + 24 a^5 b^3 c^7 OH S + 18 a^3 b^5 c^7 OH S + 8 a b^7 c^7 OH S - 6 a^5 b c^9 OH S - 30 a^3 b^3 c^9 OH S - 12 a b^5 c^9 OH S + 12 a^3 b c^11 OH S + 12 a b^3 c^11 OH S - 4 a b c^13 OH S : :

See Antreas Hatzipolakis and Francisco Javier García Capitán, euclid 6388.

X(64481) lies on these lines: {2, 3}, {542, 44124}, {1989, 8105}, {8116, 45016}, {13414, 18374}, {15360, 24651}, {32225, 44126}

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X(64482) = 8TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

Barycentrics    -2 a^12 + 6 a^10 b^2 - 13 a^8 b^4 + 5 a^6 b^6 + 7 a^4 b^8 - 5 a^2 b^10 + 2 b^12 + 6 a^10 c^2 - 2 a^8 b^2 c^2 + 11 a^6 b^4 c^2 - 19 a^4 b^6 c^2 + 7 a^2 b^8 c^2 - 9 b^10 c^2 - 13 a^8 c^4 + 11 a^6 b^2 c^4 + 6 a^4 b^4 c^4 + 22 b^8 c^4 + 5 a^6 c^6 - 19 a^4 b^2 c^6 - 30 b^6 c^6 + 7 a^4 c^8 + 7 a^2 b^2 c^8 + 22 b^4 c^8 - 5 a^2 c^10 - 9 b^2 c^10 + 2 c^12 - 2 a^10 W + 5 a^8 b^2 W + 6 a^6 b^4 W - 7 a^4 b^6 W - 4 a^2 b^8 W + 2 b^10 W + 5 a^8 c^2 W - 30 a^6 b^2 c^2 W + 14 a^4 b^4 c^2 W + 25 a^2 b^6 c^2 W - 8 b^8 c^2 W + 6 a^6 c^4 W + 14 a^4 b^2 c^4 W - 46 a^2 b^4 c^4 W + 6 b^6 c^4 W - 7 a^4 c^6 W + 25 a^2 b^2 c^6 W + 6 b^4 c^6 W - 4 a^2 c^8 W - 8 b^2 c^8 W + 2 c^10 W : : where W^2 = a^4 - a^2 b^2 + b^4 - a^2 c^2 - b^2 c^2 + c^4

See Antreas Hatzipolakis and Francisco Javier García Capitán, euclid 6388.

X(64482) lies on these lines: {2, 3}, {2028, 31862}, {3413, 6321}

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X(64483) = 9TH HATZIPOLAKIS-GARCÍA CAPITÁN-EULER POINT

Barycentrics    -2 a^12 + 6 a^10 b^2 - 13 a^8 b^4 + 5 a^6 b^6 + 7 a^4 b^8 - 5 a^2 b^10 + 2 b^12 + 6 a^10 c^2 - 2 a^8 b^2 c^2 + 11 a^6 b^4 c^2 - 19 a^4 b^6 c^2 + 7 a^2 b^8 c^2 - 9 b^10 c^2 - 13 a^8 c^4 + 11 a^6 b^2 c^4 + 6 a^4 b^4 c^4 + 22 b^8 c^4 + 5 a^6 c^6 - 19 a^4 b^2 c^6 - 30 b^6 c^6 + 7 a^4 c^8 + 7 a^2 b^2 c^8 + 22 b^4 c^8 - 5 a^2 c^10 - 9 b^2 c^10 + 2 c^12 + 2 a^10 W - 5 a^8 b^2 W - 6 a^6 b^4 W + 7 a^4 b^6 W + 4 a^2 b^8 W - 2 b^10 W - 5 a^8 c^2 W + 30 a^6 b^2 c^2 W - 14 a^4 b^4 c^2 W - 25 a^2 b^6 c^2 W + 8 b^8 c^2 W - 6 a^6 c^4 W - 14 a^4 b^2 c^4 W + 46 a^2 b^4 c^4 W - 6 b^6 c^4 W + 7 a^4 c^6 W - 25 a^2 b^2 c^6 W - 6 b^4 c^6 W + 4 a^2 c^8 W + 8 b^2 c^8 W - 2 c^10 W : : where W^2 = a^4 - a^2 b^2 + b^4 - a^2 c^2 - b^2 c^2 + c^4

See Antreas Hatzipolakis and Francisco Javier García Capitán, euclid 6388.

X(64483) lies on these lines: {2, 3}, {2029, 31863}, {3414, 6321}

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SAME CENTROID

Let ABC be a triangle and A'B'C' the cevian triangle of O

Denote

Ma, Mb, Mc = the midpoints of AA'. BB', CC', resp.

Ha, Hb, Hc = the orthocenters of OMbMc, OMcMa, OMaMb, resp,

The triangles ABC and HaHbHc share the same centroid G

APH

Francisco Javier García Capitán A triangle of orthocenters with centroid G
FJGC

AN ORTHOCENTER

Let ABC be a triangle and A'B'C' the orthic triangle

Denote

Ma, Mb, Mc = the midpoints of AA', BB', CC', resp.

Ha, Hb, Hc = the orthocenters of HMbMc, HMcMa, HMaMb, resp.

Then
Orthocenter of HaHbHc = Nine Point Circle Center N

Euclid 6368
Romantics of Geometry

PROOF

The perpendicular from Mb to HMc intersects B'C' at A". In the triangle BB'C' we have MbA" // BC' and Mb = midpoint of BB', therefore A" is the midpoint of B'C'.
Similarly in the triangle CC'B' the perpendicular from Mc to HMb passes through the midpoint of B'C'. Therefore A" is the orthocenter Ha of HMbMc.
Similarly the orthocenters Hb, Hc of HMcMa, HMaMb are the midpoints of C'A', A'B', resp., that is HaHbHc is the medial triangle of A'B'C'

The orthocenter of HaHbHc is the circumcenter of A'B'C'

The circumcenter of A'B'C' is the Nine Point Circle center N of ABC.
H of HaHbHc = O of A'B'C' = N of ABC
QED

THREE CURIOUS MIDPOINTS

Let ABC be a triangle, P a point and A'B'C' the cevian triangle of P Ma = the midpoint of AbAc. Similarly Mb, Mc
Which is the locus of P such that ABC, MaMbMc are orthologic?
Antreas Hatzipolakis

Study:
Francisco Javier García Capitán: Three curious midpoints
FJGC

BILOGIC TRIANGLES

Antreas Hatzipolakis, Bilogic Triangles by Construction
Euclid 6242

Study by Francisco Javier García Capitán: Bilogic triangles by construction

Cosmology of Plane Geometry: Concepts and Theorems

Alexander Skutin,Tran Quang Hung, Antreas Hatzipolakis, Kadir Altintas: Cosmology of Plane Geometry: Concepts and Theorems>

ΨΗΦ. Cosmology of Plane Geometry: Concepts and Theorems
ΨΗΦ. Cosmology of Plane Geometry: Concepts and Theorems

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ΨΗΦ. Cosmology of Plane Geometry: Concepts and Theorems
ΨΗΦ. Cosmology of Plane Geometry: Concepts and Theorems

Fermat-Torricelli and Napoleon Points

Thanasis Gakopoulos, Debabrata Nag: Fermat-Torricelli and Napoleon Points of a Triangle
A PLAGIOGONAL Approach

ΨΗΦ Fermat-Torricelli and Napoleon Points

A PROOF OF MORLEY THEOREM

Thanasis Gakopoulos - Debabrata Nag, Morley Theorem ̶ PLAGIOGONAL Approach of Proof

Abstract: In this work, an attempt has been made by the authors to present a PLAGIOGONAL approach to prove the Morley Theorem involving the intersecting trisectors of the angles of a scalene triangle. The objective of the present work is to also establish the non-orthogonal coordinates of the vertices of Morley triangle.

Gakopoulos - Nag

X(61637), X(61638)

X(61637) = ISOGONAL CONJUGATE Χ(61638)

Barycentrics   

See Floor van Lamoen and Francisco, euclid 6085.

X(61637) lies on this line:

X(61637) = isogonal comjugate of X(61638)

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X(61638) = X(2)X(3)∩X(195)X(15109)

Barycentrics   

See Floor van Lamoen and Francisco, euclid 6085.

X(61638) lies on these lines:

X(61638) = isogonal comjugate of X(61637)

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