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# [分享] 三角形有多少个心 (特征点)？

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faculty.evansville.edu/ck6/encyclopedia/ETC.html

X(1) = INCENTER
Trilinears    1 : 1 : 1
Barycentrics   a : b : c
Barycentrics  sin A : sin B : sin C
Tripolars    Sqrt[b c (b + c - a)] : :
Tripolars    sec A' : :, where A'B'C' is the excentral triangle
X(1) = 3R*X(2) + r*X(3) + s*cot(ω)*X(6)
X(1) = [A]/Ra + [B]/Rb + [C]/Rc - X(176)/Rs, where Ra, Rb, Rc = radii of Soddy circles, Rs = radius of inner Soddy circle, [A], [B], [C] are the vertices of ABC
X(1) = [A]/Ra + [B]/Rb + [C]/Rc - X(175)/Rs', where Ra, Rb, Rc = radii of Soddy circles, Rs' = radius of outer Soddy circle, [A], [B], [C] are the vertices of ABC
X(1) = (sin A)*[A] + (sin B)*[B] + (sin C)*[C], where [A], [B], [C] are vertices of ABC
X(1) = a*[A] + b*[B] + c*[C], where [A], [B], [C] are vertices
X(1) is the point of concurrence of the interior angle bisectors of ABC; the point inside ABC whose distances from sidelines BC, CA, AB are equal. This equal distance, r, is the radius of the incircle, given by r = 2*area(ABC)/(a + b + c).

Three more points are also equidistant from the sidelines; they are given by these names and trilinears:

A-excenter = -1 : 1 : 1,     B-excenter = 1 : -1 : 1,     C-excenter = 1 : 1 : -1.

The radii of the excircles are 2*area(ABC)/(-a + b + c), 2*area(ABC)/(a - b + c), 2*area(ABC)/(a + b - c).

If you have The Geometer's Sketchpad, you can view Incenter.
If you have GeoGebra, you can view Incenter.

Writing the A-exradius as r(a,b,c), the others are r(b,c,a) and r(c,a,b). If these exradii are abbreviated as ra, rb, rc, then 1/r = 1/ra +1/rb + 1/rc. Moreover,

area(ABC) = sqrt(r*ra*rb*rc) and ra + rb + rc = r + 4R, where R denotes the radius of the circumcircle.

The incenter is the identity of the group of triangle centers under trilinear multiplication defined by (x : y : z)*(u : v : w) = xu : yv : zw.

A construction for * is easily obtained from the construction for "barycentric multiplication" mentioned in connection with X(2), just below.

The incenter and the other classical centers are discussed in these highly recommended books:

Paul Yiu, Introduction to the Geometry of the Triangle, 2002;
Nathan Altshiller Court, College Geometry, Barnes & Noble, 1952;
Roger A. Johnson, Advanced Euclidean Geometry, Dover, 1960.

Let OA be the circle tangent to side BC at its midpoint and to the circumcircle on the side of BC opposite A. Define OB and OC cyclically. Let LA be the external tangent to circles OB and OC that is nearest to OA. Define LB and LC cyclically. Let A' = LB ∩LC, and define B' and C' cyclically. Then triangle A'B'C' is homothetic to the medial triangle, and the center of homothety is X(1); see the reference at X(1001).

Let A'B'C' and A"B"C" be the intouch and excentral triangles; X(1) is the radical center of the circumcircles of AA'A", BB'B", CC'C". (Randy Hutson, December 10, 2016)

Let A'B'C' be the Feuerbach triangle. Let A" be the trilinear pole of line B'C', and define B" and C" cyclically. The lines AA", BB", CC" concur in X(1). (Randy Hutson, November 17, 2019)

Let A'B'C' be the mixtilinear excentral triangle. Let A" be the cevapoint of B' and C', and define B" and C" cyclically. The lines AA", BB", CC" concur in X(1). (Randy Hutson, November 17, 2019)

Let A'B'C' be the mixtilinear excentral triangle. Let A" be the trilinear pole of line B'C', and define B" and C" cyclically. The lines AA", BB", CC" concur in X(1). (Randy Hutson, November 17, 2019)

Let A'B'C' be the mixtilinear excentral triangle. Let LA be the trilinear polar of A', and define LB and LC cyclically. Let A" = LB∩LC, and define B" and C" cyclically. The lines AA", BB", CC" concur in X(1). (Randy Hutson, November 17, 2019)

Let OA be the circle centered at the A-vertex of the excenters-midpoints triangle and passing through A; define OB and OC cyclically. X(1) is the radical center of OA, OB, OC. (Randy Hutson, August 30, 2020)

Let OA be the circle centered at the A-vertex of the Gemini triangle 22 and passing through A; define OB and OC cyclically. X(1) is the radical center of OA, OB, OC. (Randy Hutson, August 30, 2020)

X(1) lies on all Z-cubics (e.g., Thomson, Darboux, Napoleon, Neuberg) and these lines: 2,8   3,35   4,33   5,11   6,9   7,20   15,1251   16,1250   19,28   21,31   24,1061   25,1036   29,92   30,79   32,172   39,291   41,101   49,215   54,3460   60,110   61,203   62,202   64,1439   69,1245   71,579   74,3464   75,86   76,350   82,560   84,221   87,192   88,100   90,155   99,741   102,108   104,109   142,277   147,150   159,1486   163,293   164,258   166,1488   167,174   168,173   179,1142   181,970   182,983   184,1726   185,296   188,361   190,537   195,3467   196,207   201,212   204,1712   210,2334   224,377   227,1465   228,1730   229,267   256,511   257,385   280,1256   281,282   289,363   312,1089   318,1897   320,752   321,964   329,452   335,384   336,811   341,1050   344,1265   346,1219   357,1508   358,1507   364,365   371,1702   372,1703   376,553   378,1063   393,836   394,1711   399,3065   409,1247   410,1248   411,1254   442,1834   474,1339   475,1861   512,875   513,764   514,663   522,1459   528,1086   561,718   563,1820   564,1048   572,604   573,941   574,1571   594,1224   607,949   615,3300   631,1000   644,1280   647,1021   650,1643   651,1156   659,891   662,897   672,1002   689,719   704,1502   727,932   731,789   748,756   761,825   765,1052   810,1577   840,1308   905,1734   908,998   921,1800   939,1260   945,1875   947,1753   951,1435   969,1444   971,1419   989,1397   1013,1430   1037,1041   1053,1110   1057,1598   1059,1597   1073,3341   1075,1148   1106,1476   1157,3483   1168,1318   1170,1253   1185,1206   1197,1613   1292,1477   1333,1761   1342,1700   1343,1701   1361,1364   1389,1393   1399,1727   1406,1480   1409,1765   1437,1710   1472,1791   1719,1790   1855,1886   1859,1871   1872,1887   2120,3461   2130,3347   3183,3345   3342,3343   3344,3351   3346,3353   3348,3472   3350,3352   3354,3355   3462,3469

X(1) is the {X(2),X(8)}-harmonic conjugate of X(10). For a list of other harmonic conjugates of X(1), click Tables at the top of this page.

X(1) = midpoint of X(i) and X(j) for these (i,j): (3, 1482), (7,390), (8,145), (55,2099), (56,2098)
X(1) = reflection of X(i) in X(j) for these (i,j): (2,551), (3,1385), (4,946), (6,1386), (8,10), (9,1001), (10,1125), (11,1387), (36,1319), (40,3), (43,995), (46,56), (57,999), (63,993), (65,942), (72,960), (80,11), (100,214), (191,21), (200,997), (238,1279), (267,229), (291,1015), (355,5), (484,36), (984,37), (1046,58), (1054,106), (1478,226)
X(1) = isogonal conjugate of X(1)
X(1) = isotomic conjugate of X(75)
X(1) = cyclocevian conjugate of X(1029)
X(1) = circumcircle-inverse of X(36)
X(1) = Fuhrmann-circle-inverse of X(80)
X(1) = Bevan-circle-inverse of X(484)
X(1) = Spieker-radical-circle-inverse of X(38471)
X(1) = complement of X(8)
X(1) = anticomplement of X(10)
X(1) = anticomplementary conjugate of X(1330)
X(1) = complementary conjugate at X(1329)
X(1) = eigencenter of cevian triangle of X(i) for I = 1, 88, 100, 162, 190
X(1) = eigencenter of anticevian triangle of X(i) for I = 1, 44, 513
X(1) = exsimilicenter of inner and outer Soddy circles; insimilicenter is X(7)
X(1) = X(i)-Ceva conjugate of X(j) for these (i,j): (2,9), (4,46), (6,43), (7,57), (8,40), (9,165), (10,191), (21,3), (29,4), (75,63), (77,223), (78,1490), (80,484), (81,6), (82,31), (85,169), (86,2), (88,44), (92,19), (100,513), (104,36), (105,238), (174,173), (188,164), (220,170), (259,503), (266,361), (280,84), (366,364), (508,362), (1492,1491)
X(1) = cevapoint of X(i) and X(j) for these (i,j):
(2,192), (6,55), (11,523), (15,202), (16,203), (19,204), (31,48), (34,207), (37,42), (50,215), (56,221), (65,73), (244,513)
X(1) = X(i)-cross conjugate of X(j) for these (i,j): (2,87), (3,90), (6,57), (31,19), (33,282), (37,2), (38,75), (42,6), (44,88), (48,63), (55,9), (56,84), (58,267), (65,4), (73,3), (192,43), (207,1490), (221,40), (244,513), (259,258), (266,505), (354,7), (367,366), (500,35), (513,100), (517,80), (518,291), (1491,1492)
X(1) = crosspoint of X(i) and X(j) for these (i,j): (2,7), (8,280), (21,29), (59,110), (75,92), (81,86)
X(1) = crosssum of X(i) and X(j) for these (i,j): (2,192), (4,1148), (6,55), (11,523), (15,202), (16,203), (19,204), (31,48), (34,207), (37,42), (44,678), (50,215), (56,221), (57,1419), (65,73), (214,758), (244,513), (500,942), (512,1015), (774,820), (999,1480)
X(1) = crossdifference of every pair of points on line X(44)X(513)
X(1) = X(i)-Hirst inverse of X(j) for these (i,j): (2,239), (4,243), (6,238), (9,518), (19,240), (57,241), (105,294), (291,292)
X(1) = X(6)-line conjugate of X(44)
X(1) = X(i)-aleph conjugate of X(j) for these (i,j):
(1,1), (2,63), (4,920), (21,411), (29,412), (88,88), (100,100), (162,162), (174,57), (188,40), (190,190), (266,978), (365,43), (366,9), (507,173), (508,169), (513,1052), (651, 651), (653,653), (655,655), (658,658), (660,660), (662,662), (673,673), (771,771), (799,799), (823,823), (897,897)
X(1) = X(i)-beth conjugate of X(j) for these (i,j): (1,56), (2,948), (8,8), (9,45), (21,1), (29,34), (55,869), (99,85), (100,1), (110,603), (162,208), (643,1), (644,1), (663,875), (664,1), (1043,78)
X(1) = insimilicenter of 1st & 2nd Johnson-Yff circles (the exsimilicenter is X(4))
X(1) = orthic-isogonal conjugate of X(46)
X(1) = excentral-isogonal conjugate of X(40)
X(1) = excentral-isotomic conjugate of X(2951)
X(1) = center of Conway circle
X(1) = center of Adams circle
X(1) = X(3) of polar triangle of Conway circle
X(1) = homothetic center of intangents triangle and reflection of extangents triangle in X(3)
X(1) = Hofstadter 1/2 point
X(1) = orthocenter of X(4)X(9)X(885)
X(1) = intersection of tangents at X(7) and X(8) to Lucas cubic K007
X(1) = trilinear product of vertices of 2nd mixtilinear triangle
X(1) = trilinear product of vertices of 2nd Sharygin triangle
X(1) = homothetic center of Mandart-incircle triangle and 2nd isogonal triangle of X(1); see X(36)
X(1) = trilinear pole of the antiorthic axis (which is also the Monge line of the mixtilinear excircles)
X(1) = pole wrt polar circle of trilinear polar of X(92) (line X(240)X(522))
X(1) = X(48)-isoconjugate (polar conjugate) of X(92)
X(1) = X(6)-isoconjugate of X(2)
X(1) = trilinear product of PU(i) for these i: 1, 17, 114, 115, 118, 119, 113
X(1) = barycentric product of PU(i) for these i: 6, 124
X(1) = vertex conjugate of PU(9)
X(1) = bicentric sum of PU(i) for these i: 28, 47, 51, 55, 64
X(1) = trilinear pole of PU(i) for these i: 33, 50, 57, 58, 74, 76, 78
X(1) = crossdifference of PU(i) for these i: 33, 50, 57, 58, 74, 76, 78
X(1) = midpoint of PU(i) for these i: 47, 51, 55
X(1) = PU(28)-harmonic conjugate of X(1023)
X(1) = PU(64)-harmonic conjugate of X(351)
X(1) = intersection of diagonals of trapezoid PU(6)PU(31)
X(1) = perspector circumconic centered at X(9)
X(1) = eigencenter of mixtilinear excentral triangle
X(1) = eigencenter of 2nd Sharygin triangle
X(1) = perspector of ABC and unary cofactor triangle of extangents triangle
X(1) = perspector of ABC and unary cofactor triangle of Feuerbach triangle
X(1) = perspector of ABC and unary cofactor triangle of Apollonius triangle
X(1) = perspector of ABC and unary cofactor triangle of 2nd mixtilinear triangle
X(1) = perspector of ABC and unary cofactor triangle of 4th mixtilinear triangle
X(1) = perspector of ABC and unary cofactor triangle of Apus triangle
X(1) = perspector of unary cofactor triangles of 6th and 7th mixtilinear triangles
X(1) = perspector of unary cofactor triangles of 2nd and 3rd extouch triangles
X(1) = perspector of 5th mixtilinear triangle and unary cofactor triangle of 2nd mixtilinear triangle
X(1) = perspector of 5th mixtilinear triangle and unary cofactor triangle of 4th mixtilinear triangle
X(1) = X(3)-of-reflection-triangle-of-X(1)
X(1) = X(1181)-of-2nd-extouch triangle
X(1) = perspector of ABC and orthic-triangle-of-2nd-circumperp-triangle
X(1) = X(4)-of-excentral triangle
X(1) = X(40)-of-Yff central triangle
X(1) = X(20)-of-1st circumperp triangle
X(1) = X(4)-of-2nd circumperp triangle
X(1) = X(4)-of-Fuhrmann triangle
X(1) = X(100)-of-X(1)-Brocard triangle
X(1) = antigonal image of X(80)
X(1) = trilinear pole wrt excentral triangle of antiorthic axis
X(1) = trilinear pole wrt incentral triangle of antiorthic axis
X(1) = Miquel associate of X(7)
X(1) = homothetic center of Johnson triangle and cross-triangle of ABC and 2nd isogonal triangle of X(1)
X(1) = homothetic center of 1st Johnson-Yff triangle and cross-triangle of ABC and 2nd isogonal triangle of X(1)
X(1) = homothetic center of 2nd Johnson-Yff triangle and cross-triangle of ABC and 2nd isogonal triangle of X(1)
X(1) = homothetic center of Mandart-incircle triangle and cross-triangle of ABC and 1st Johnson-Yff triangle
X(1) = homothetic center of medial triangle and cross-triangle of Aquila and anti-Aquila triangles
X(1) = homothetic center of outer Garcia triangle and cross-triangle of Aquila and anti-Aquila triangles
X(1) = X(8)-of-cross-triangle-of Aquila-and-anti-Aquila-triangles
X(1) = X(3)-of-Mandart-incircle-triangle
X(1) = X(100)-of-inner-Garcia-triangle
X(1) = Thomson-isogonal conjugate of X(165)
X(1) = X(8)-of-outer-Garcia-triangle
X(1) = X(486)-of-BCI-triangle
X(1) = X(164)-of-orthic-triangle if ABC is acute
X(1) = X(1593)-of-Ascella-triangle
X(1) = excentral-to-Ascella similarity image of X(1697)
X(1) = Dao image of X(1)
X(1) = X(40)-of-reflection of ABC in X(3)
X(1) = radical center of the tangent circles of ABC
X(1) = homothetic center of intangents triangle and anti-tangential midarc triangle
X(1) = K(X(15)) = K(X(16)), as defined at X(174)
X(1) = X(3)-of-hexyl-triangle
X(1) = eigencenter of trilinear obverse triangle of X(2)
X(1) = hexyl-isogonal conjugate of X(40)
X(1) = inverse-in-polar-circle of X(1785)
X(1) = inverse-in-orthoptic-circle-of-Steiner-inellipse of X(5121)
X(1) = inverse-in-OI-inverter of X(1155)
X(1) = inverse-in-Steiner-circumellipse of X(239)
X(1) = inverse-in-MacBeath-circumconic of X(2323)
X(1) = inverse-in-circumconic-centered-at-X(9) of X(44)
X(1) = excentral-to-ABC barycentric image of X(40)
X(1) = excentral-to-ABC functional image of X(164)
X(1) = excentral-to-ABC trilinear image of X(164)
X(1) = orthic-to-ABC functional image of X(4), if ABC is acute
X(1) = orthic-to-ABC trilinear image of X(4), if ABC is acute
X(1) = intouch-to-ABC barycentric image of X(1)
X(1) = excentral-to-intouch similarity image of X(40)
X(1) = ABC-to-excentral barycentric image of X(8)
X(1) = X(1)-vertex conjugate of X(56)
X(1) = perspector of ABC and reflection triangle of intangents triangle
X(1) = perspector of pedal and anticevian triangles of X(40)
X(1) = perspector of hexyl triangle and antipedal triangle of X(40)
X(1) = perspector of hexyl triangle and anticevian triangle of X(57)
X(1) = X(4)-of-Pelletier-triangle

楼主| 发表于 2022-6-6 22:39:53 | 显示全部楼层
 ① 前 9 行是什么意思？ Trilinears    1 : 1 : 1 Barycentrics   a : b : c Barycentrics  sin A : sin B : sin C Tripolars    Sqrt[b c (b + c - a)] : : Tripolars    sec A' : :, where A'B'C' is the excentral triangle X(1) = 3R*X(2) + r*X(3) + s*cot(ω)*X(6) X(1) = [A]/Ra + [B]/Rb + [C]/Rc - X(176)/Rs, where Ra, Rb, Rc = radii of Soddy circles, Rs = radius of inner Soddy circle, [A], [B], [C] are the vertices of ABC X(1) = [A]/Ra + [B]/Rb + [C]/Rc - X(175)/Rs', where Ra, Rb, Rc = radii of Soddy circles, Rs' = radius of outer Soddy circle, [A], [B], [C] are the vertices of ABC X(1) = (sin A)*[A] + (sin B)*[B] + (sin C)*[C], where [A], [B], [C] are vertices of ABC X(1) = a*[A] + b*[B] + c*[C], where [A], [B], [C] are vertices ② X(1) = midpoint of X(i) and X(j) for these (i,j): (3, 1482), (7,390), (8,145), (55,2099), (56,2098) 是什么意思？ ③

### 点评

 平面上的一个三角形有无穷多个"心".

 上面显示的ETC，是一个关于三角形“心”汇总表，大约有5000多个

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