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Nine-point circle

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623: 558: 20: 205: 1228:. The remaining six intersection points of these nine-point circles each concur with the midpoints of the four triangles. Remarkably, there exists a unique nine-point conic, centered at the centroid of these four arbitrary points, that passes through all seven points of intersection of these nine-point circles. Furthermore, because of the Feuerbach conic theorem mentioned above, there exists a unique rectangular 353: 293: 28: 1193:
The centers of the incircle and excircles of a triangle form an orthocentric system. The nine-point circle created for that orthocentric system is the circumcircle of the original triangle. The feet of the altitudes in the orthocentric system are the vertices of the original
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and three "diagonal points" where opposite sides of the quadrilateral intersect. There are six "sidelines" in the quadrilateral; the nine-point conic intersects the midpoints of these and also includes the diagonal points. The conic is an
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did not entirely discover the nine-point circle, but rather the six-point circle, recognizing the significance of the midpoints of the three sides of the triangle and the feet of the altitudes of that triangle.
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by Clark Kimberling. The nine-point center is indexed as X(5), the Feuerbach point, as X(11), the center of the Kiepert hyperbola as X(115), and the center of the Jeřábek hyperbola as X(125).
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of the cyclic quadrilateral. The nine-point circles are all congruent with a radius of half that of the cyclic quadrilateral's circumcircle. The nine-point circles form a set of four
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is given, then the four triangles formed by any combination of three distinct points of that system all share the same nine-point circle. This is a consequence of symmetry: the
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himself proved the existence of the circle. He was the first to recognize the added significance of the three midpoints between the triangle's vertices and the orthocenter. (
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Eigenschaften einiger merkwürdigen Punkte des geradlinigen Dreiecks und mehrerer durch sie bestimmten Linien und Figuren. Eine analytisch-trigonometrische Abhandlung
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from that second triangle. A third midpoint lies on their common side. (The same 'midpoints' defining separate nine-point circles, those circles must be concurrent.)
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that pass through the vertices of a triangle lies on its nine-point circle. Examples include the well-known rectangular hyperbolas of
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A nine-point circle bisects a line segment going from the corresponding triangle's orthocenter to any point on its circumcircle.
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and the nine-point circle is an instance of the general nine-point conic that has been constructed with relation to a triangle
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is in one of the three adjacent regions, and the hyperbola is rectangular when P lies on the circumcircle of
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Note that the construction still works even if the orthocenter and circumcenter fall outside of the triangle.
1560:{\displaystyle {\frac {(b^{2}-c^{2})^{2}}{a}}:{\frac {(c^{2}-a^{2})^{2}}{b}}:{\frac {(a^{2}-b^{2})^{2}}{c}}} 1180:{\displaystyle {\overline {PA}}^{2}+{\overline {PB}}^{2}+{\overline {PC}}^{2}+{\overline {PH}}^{2}=4R^{2}.} 245:
two of the altitudes have feet outside the triangle, but these feet still belong to the nine-point circle.
937:{\displaystyle {\overline {PA}}^{2}+{\overline {PB}}^{2}+{\overline {PC}}^{2}+{\overline {PH}}^{2}=K^{2},} 787:{\displaystyle {\overline {NA}}^{2}+{\overline {NB}}^{2}+{\overline {NC}}^{2}+{\overline {NH}}^{2}=3R^{2}} 553:. The point of intersection of the bimedians of the cyclic quadrilateral belongs to the nine-point circle. 2466:
Generalizes nine-point circle to a nine-point conic with an associated generalization of the Euler line.
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The nine-point circle of a reference triangle is the circumcircle of both the reference triangle's
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Discusses the nine-point circle with regard to three different quadratic forms (blue, red, green).
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College Geometry: An Introduction to the Modern Geometry of the Triangle and the Circle
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be a variable point in trilinear coordinates, an equation for the nine-point circle is
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In 1822 Karl Feuerbach discovered that any triangle's nine-point circle is externally
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The diagram above shows the nine significant points of the nine-point circle. Points
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of one triangle adjacent to a vertex that is an orthocenter to another triangle are
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are given that do not form an orthocentric system, then the nine-point circles of
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had stated and proven the same theorem.) But soon after Feuerbach, mathematician
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Fraivert, David (July 2019). "New points that belong to the nine-point circle".
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Consequently, these four triangles have circumcircles with identical radii. Let
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Ein einfacher Beweis für den Satz von Feuerbach mit koordinatenfreien Vektoren
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History about the nine-point circle based on J.S. MacKay's article from 1892:
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Fraivert, David (2019), "New points that belong to the nine-point circle",
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The nine point circle and the 16 tangent circles of the orthocentric system
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the nine-point center. Furthermore the nine-point circle is the locus of
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of lines passing through the circumcenter lie on the nine-point circle.
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at which the incircle and the nine-point circle touch is called the
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be an arbitrary point in the plane of the orthocentric system. Then
309: 305: 284:.) Thus, Terquem was the first to use the name nine-point circle. 108: 92: 80: 603:(with vertices at the feet of the reference triangle's altitudes). 1967: 1573:
Trilinear coordinates for the center of the Jeřábek hyperbola are
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and Feuerbach. This fact is known as the Feuerbach conic theorem.
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of the nine-point circle bisects a segment from the orthocenter
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The nine-point circle is tangent to the incircle and excircles.
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are the midpoints of the line segments between each altitude's
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are the midpoints of the three sides of the triangle. Points
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is twice the radius of that triangle's nine-point circle.
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be the nine-point circle of the diagonal triangle of a
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A triangle's circumcircle, its nine-point circle, its
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are the feet of the altitudes of the triangle. Points
2372:"A Javascript demonstration of the nine point circle" 1763: 1585: 1415: 1318: 1060: 968: 820: 670: 489: 408: 2273: 2130: 1361:{\displaystyle {\overline {ON}}=2{\overline {NM}}.} 532:{\displaystyle {\overline {HN}}=3{\overline {NG}}.} 2410: 1907: 1723: 1559: 1360: 1179: 1016: 936: 786: 531: 448:{\displaystyle {\overline {ON}}={\overline {NH}}.} 447: 2483: 2253: 2237: 2225: 2098:) give a proof of the Nine-Point Circle Theorem. 2047: 2460:Nine-point conic and Euler line generalization 2149:Posamentier, Alfred S., and Lehmann, Ingmar. 1298:lies on the line connecting the circumcenter 2107: 654:represent the common nine-point center and 253:Although he is credited for its discovery, 198: 2117:A Sequel to the First Six Books of Euclid 338:Other properties of the nine-point circle 2342: 2312: 2287:(Monograph ed.), Nürnberg: Wiessner 2199: 2164: 621: 556: 291: 230:) and the triangle's orthocenter (point 140:The nine-point circle is also known as 26: 18: 2456:from the Wolfram Demonstrations Project 2448:Special lines and circles in a triangle 2072:Kocik, Jerzy; Solecki, Andrzej (2009). 2484: 1274:to the reference cyclic quadrilateral 99:defined from the triangle. These nine 91:that can be constructed for any given 2411: 2392: 2094:Kocik and Solecki (sharers of a 2010 2454:Interactive Nine Point Circle applet 2145: 2143: 2141: 2139: 954:is kept constant, then the locus of 583:belongs to the nine-point circle of 579:of intersection of the bimedians of 392:(making the orthocenter a center of 2292: 2059: 1957:. The vertices of the triangle and 465:is one-fourth of the way along the 13: 287: 16:Circle constructed from a triangle 14: 2503: 2379:Encyclopedia of Triangles Centers 2365: 2353:International Journal of Geometry 2279:Buzengeiger, Carl Heribert Ignatz 2254:Altshiller-Court, Nathan (1925), 2209:International Journal of Geometry 2136: 1920: 1243:, then the nine-point circles of 265:.) (At a slightly earlier date, 2387:History of the Nine Point Circle 2131:Feuerbach & Buzengeiger 1822 366: 351: 203: 2470:N J Wildberger. Chromogeometry. 2231: 1931:The circle is an instance of a 1036:for the corresponding constant 2492:Circles defined for a triangle 2219: 2193: 2158: 2101: 2065: 2053: 2041: 1896: 1842: 1718: 1706: 1690: 1684: 1672: 1660: 1644: 1638: 1626: 1614: 1598: 1592: 1542: 1515: 1494: 1467: 1446: 1419: 1385:, and the circumcircle of its 308:and internally tangent to its 1: 2475:Stefan Götz, Franz Hofbauer: 2247: 2115:Nine-Point Circle Theorem, in 2012:, a related construction for 2439:Feuerbach's Theorem: a Proof 1350: 1329: 1147: 1122: 1097: 1072: 907: 882: 857: 832: 757: 732: 707: 682: 571:is the diagonal triangle of 521: 500: 437: 419: 248: 111:of each side of the triangle 7: 2003: 564:is a cyclic quadrilateral. 343:The radius of a triangle's 10: 2508: 2299:Holt, Rinehart and Winston 2258:(2nd ed.), New York: 2074:"Disentangling a Triangle" 1924: 1294:and its homothetic center 312:; this result is known as 2464:Dynamic Geometry Sketches 2430:Nine Point Circle in Java 2155:, Prometheus Books, 2012. 1985:with the triangle, but a 1197:If four arbitrary points 304:to that triangle's three 2343:Fraivert, David (2018), 2316:The Mathematical Gazette 2200:Fraivert, David (2018). 2167:The Mathematical Gazette 2152:The Secrets of Triangles 2090:10.4169/193009709x470065 2034: 958:is a circle centered at 2275:Feuerbach, Karl Wilhelm 1981:or in a region sharing 1220:concur at a point, the 199:Nine significant points 132:of the triangle to the 2293:Kay, David C. (1969), 2238:Altshiller-Court (1925 2226:Altshiller-Court (1925 2048:Altshiller-Court (1925 1963:complete quadrilateral 1950:is the orthocenter of 1909: 1725: 1561: 1399:for the center of the 1362: 1239:are given that form a 1181: 1018: 938: 788: 627: 608:rectangular hyperbolas 591: 533: 461:The nine-point center 449: 322: 297: 255:Karl Wilhelm Feuerbach 146:Karl Wilhelm Feuerbach 76: 24: 1910: 1726: 1562: 1397:Trilinear coordinates 1363: 1182: 1019: 939: 789: 625: 560: 534: 450: 318: 295: 226:intersection (points 30: 22: 2096:Lester R. Ford Award 1987:nine-point hyperbola 1761: 1583: 1413: 1316: 1241:cyclic quadrilateral 1058: 966: 818: 668: 551:cyclic quadrilateral 487: 406: 271:Jean-Victor Poncelet 191:. Its center is the 170:twelve-points circle 124:The midpoint of the 35: Triangle sides 2397:"Nine-Point Circle" 2329:10.1017/mag.2019.53 2179:10.1017/mag.2019.53 2078:Amer. Math. Monthly 2062:, pp. 18, 245) 2050:, pp. 103–110) 1942:and a fourth point 1387:tangential triangle 633:orthocentric system 473:to the orthocenter 314:Feuerbach's theorem 181:medioscribed circle 2413:Weisstein, Eric W. 2394:Weisstein, Eric W. 2260:Barnes & Noble 2029:Synthetic geometry 2014:circular triangles 1905: 1721: 1557: 1358: 1302:to the anticenter 1177: 1014: 979: 934: 784: 628: 606:The center of all 592: 529: 469:from the centroid 445: 316:. He proved that: 298: 279:See Fig. 1, points 260:See Fig. 1, points 142:Feuerbach's circle 77: 25: 1555: 1507: 1459: 1401:Kiepert hyperbola 1353: 1332: 1150: 1125: 1100: 1075: 1040:, collapses onto 1009: 978: 910: 885: 860: 835: 760: 735: 710: 685: 524: 503: 440: 422: 396:to both circles): 267:Charles Brianchon 195:of the triangle. 193:nine-point center 166:six-points circle 85:nine-point circle 71:nine-point center 69:(centered at the 67:Nine-point circle 2499: 2426: 2425: 2407: 2406: 2361: 2349: 2339: 2323:(557): 222–232, 2309: 2295:College Geometry 2288: 2270: 2241: 2235: 2229: 2223: 2217: 2216: 2206: 2197: 2191: 2190: 2173:(557): 222–232. 2162: 2156: 2147: 2134: 2128: 2122: 2121: 2105: 2099: 2093: 2069: 2063: 2057: 2051: 2045: 2019:Lester's theorem 1999: 1992: 1980: 1973: 1960: 1956: 1949: 1945: 1941: 1927:Nine-point conic 1914: 1912: 1911: 1906: 1823: 1822: 1798: 1797: 1773: 1772: 1750: 1730: 1728: 1727: 1722: 1702: 1701: 1656: 1655: 1610: 1609: 1566: 1564: 1563: 1558: 1556: 1551: 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428: 423: 418: 410: 391: 384: 380: 370: 355: 283: 264: 263:D, E, F, G, H, I 233: 229: 221: 217: 213: 207: 189:circum-midcircle 176: 158:Terquem's circle 97:concyclic points 64: 54: 40: 34: 2507: 2506: 2502: 2501: 2500: 2498: 2497: 2496: 2482: 2481: 2450:by Walter Fendt 2368: 2347: 2250: 2245: 2244: 2236: 2232: 2224: 2220: 2204: 2198: 2194: 2163: 2159: 2148: 2137: 2129: 2125: 2106: 2102: 2070: 2066: 2058: 2054: 2046: 2042: 2037: 2006: 1994: 1990: 1983:vertical angles 1975: 1974:is interior to 1971: 1958: 1951: 1947: 1943: 1936: 1929: 1923: 1818: 1814: 1793: 1789: 1768: 1764: 1762: 1759: 1758: 1738: 1697: 1693: 1651: 1647: 1605: 1601: 1584: 1581: 1580: 1545: 1541: 1535: 1531: 1522: 1518: 1514: 1512: 1497: 1493: 1487: 1483: 1474: 1470: 1466: 1464: 1449: 1445: 1439: 1435: 1426: 1422: 1418: 1416: 1414: 1411: 1410: 1342: 1340: 1321: 1319: 1317: 1314: 1313: 1303: 1299: 1295: 1288: 1285: 1282: 1281: 1279: 1275: 1268:Johnson circles 1244: 1236: 1235:If four points 1225: 1202: 1198: 1168: 1164: 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239:acute triangle 200: 197: 154:Leonhard Euler 150:Euler's circle 138: 137: 122: 112: 61: 51: 37: 31: 15: 9: 6: 4: 3: 2: 2504: 2493: 2490: 2489: 2487: 2478: 2474: 2471: 2468: 2465: 2461: 2458: 2455: 2452: 2449: 2446: 2444: 2440: 2437: 2435: 2431: 2428: 2423: 2422: 2417: 2414: 2409: 2404: 2403: 2398: 2395: 2390: 2388: 2384: 2381: 2380: 2376: 2373: 2370: 2369: 2359: 2355: 2354: 2346: 2341: 2338: 2334: 2330: 2326: 2322: 2318: 2317: 2311: 2308: 2304: 2300: 2296: 2291: 2286: 2285: 2280: 2276: 2272: 2269: 2265: 2261: 2257: 2252: 2251: 2239: 2234: 2228:, p. 98) 2227: 2222: 2214: 2210: 2203: 2196: 2188: 2184: 2180: 2176: 2172: 2168: 2161: 2154: 2153: 2146: 2144: 2142: 2140: 2132: 2127: 2119: 2118: 2114: 2110: 2104: 2097: 2091: 2087: 2083: 2079: 2075: 2068: 2061: 2056: 2049: 2044: 2040: 2030: 2027: 2025: 2022: 2020: 2017: 2015: 2011: 2008: 2007: 2001: 1998: 1988: 1984: 1979: 1969: 1964: 1955: 1940: 1934: 1933:conic section 1928: 1902: 1899: 1893: 1890: 1887: 1884: 1881: 1878: 1875: 1872: 1869: 1866: 1863: 1860: 1857: 1854: 1851: 1848: 1845: 1839: 1836: 1833: 1830: 1827: 1824: 1819: 1815: 1811: 1808: 1805: 1802: 1799: 1794: 1790: 1786: 1783: 1780: 1777: 1774: 1769: 1765: 1757: 1756: 1755: 1754: 1749: 1745: 1741: 1736: 1735: 1715: 1712: 1709: 1703: 1698: 1694: 1687: 1681: 1678: 1675: 1669: 1666: 1663: 1657: 1652: 1648: 1641: 1635: 1632: 1629: 1623: 1620: 1617: 1611: 1606: 1602: 1595: 1589: 1586: 1579: 1578: 1577: 1576: 1572: 1571: 1552: 1546: 1536: 1532: 1528: 1523: 1519: 1509: 1504: 1498: 1488: 1484: 1480: 1475: 1471: 1461: 1456: 1450: 1440: 1436: 1432: 1427: 1423: 1409: 1408: 1407: 1406: 1402: 1398: 1395: 1392: 1388: 1384: 1380: 1377: 1373: 1372: 1355: 1346: 1343: 1337: 1334: 1325: 1322: 1312: 1311: 1310: 1309: 1273: 1269: 1265: 1260: 1256: 1252: 1248: 1242: 1234: 1231: 1223: 1218: 1214: 1210: 1206: 1196: 1192: 1191: 1174: 1169: 1165: 1161: 1158: 1153: 1143: 1140: 1133: 1128: 1118: 1115: 1108: 1103: 1093: 1090: 1083: 1078: 1068: 1065: 1054: 1053: 1052: 1051: 1032:the locus of 1011: 1004: 1000: 996: 993: 988: 984: 975: 972: 949: 948: 931: 926: 922: 918: 913: 903: 900: 893: 888: 878: 875: 868: 863: 853: 850: 843: 838: 828: 825: 814: 813: 812: 811: 807: 799: 798: 779: 775: 771: 768: 763: 753: 750: 743: 738: 728: 725: 718: 713: 703: 700: 693: 688: 678: 675: 664: 663: 662: 661: 649: 646: 642: 634: 630: 629: 624: 617: 613: 609: 605: 602: 598: 594: 593: 588: 569: 559: 552: 544: 543: 526: 517: 514: 508: 505: 496: 493: 483: 482: 481: 480: 468: 460: 459: 442: 433: 430: 424: 415: 412: 402: 401: 400: 399: 395: 388: 376: 375: 374: 373: 369: 361: 360: 359: 358: 354: 346: 342: 341: 335: 333: 329: 324: 321: 317: 315: 311: 307: 303: 294: 285: 280: 276: 272: 268: 261: 256: 246: 244: 240: 235: 225: 208: 206: 196: 194: 190: 186: 182: 178: 177:-point circle 171: 167: 163: 159: 155: 151: 147: 143: 135: 131: 127: 123: 121: 117: 113: 110: 106: 105: 104: 102: 98: 94: 90: 86: 82: 72: 68: 58: 48: 44: 29: 21: 2443:cut-the-knot 2434:cut-the-knot 2419: 2400: 2378: 2374:at rykap.com 2357: 2351: 2320: 2314: 2297:, New York: 2294: 2283: 2255: 2233: 2221: 2212: 2208: 2195: 2170: 2166: 2160: 2150: 2126: 2116: 2113: 2103: 2081: 2077: 2067: 2055: 2043: 1996: 1989:occurs when 1977: 1961:determine a 1953: 1938: 1930: 1747: 1743: 1739: 1383:polar circle 1258: 1254: 1250: 1246: 1216: 1212: 1208: 1204: 806:circumradius 644: 640: 586: 575:. The point 567: 387:circumcenter 371: 365: 356: 350: 345:circumcircle 325: 323: 319: 299: 278: 275:Olry Terquem 259: 252: 236: 209: 202: 188: 184: 180: 173: 169: 165: 162:Olry Terquem 157: 149: 141: 139: 126:line segment 84: 78: 66: 57:circumcenter 2416:"Orthopole" 2109:Casey, John 2010:Hart circle 1230:circumconic 1028:approaches 377:The center 134:orthocenter 47:orthocenter 2248:References 2215:(1): 5–16. 1272:homothetic 1264:anticenter 1237:A, B, C, D 1226:A, B, C, D 1199:A, B, C, D 637:A, B, C, H 467:Euler line 185:mid circle 128:from each 2421:MathWorld 2402:MathWorld 2360:(1): 5–16 2337:213935239 2187:213935239 2060:Kay (1969 1891:⁡ 1873:⁡ 1855:⁡ 1837:− 1828:⁡ 1803:⁡ 1778:⁡ 1713:− 1704:⁡ 1682:⁡ 1667:− 1658:⁡ 1636:⁡ 1621:− 1612:⁡ 1590:⁡ 1529:− 1481:− 1433:− 1376:orthopole 1351:¯ 1330:¯ 1194:triangle. 1148:¯ 1123:¯ 1098:¯ 1073:¯ 1048:such that 994:− 908:¯ 883:¯ 858:¯ 833:¯ 758:¯ 733:¯ 708:¯ 683:¯ 522:¯ 501:¯ 438:¯ 420:¯ 306:excircles 249:Discovery 43:Altitudes 2486:Category 2307:69012075 2281:(1822), 2268:52013504 2111:(1886). 2004:See also 1746: : 1742: : 1737:Letting 808:; and if 645:segments 394:dilation 372:Figure 4 357:Figure 3 310:incircle 120:altitude 118:of each 109:midpoint 93:triangle 81:geometry 1968:ellipse 1292:⁠ 1280:⁠ 616:Jeřábek 612:Keipert 385:to the 302:tangent 282:J, K, L 237:For an 228:A, B, C 220:J, K, L 216:G, H, I 212:D, E, F 187:or the 164:), the 160:(after 152:(after 144:(after 2335:  2305:  2266:  2185:  1391:coaxal 950:where 800:where 631:If an 224:vertex 183:, the 179:, the 172:, the 168:, the 130:vertex 101:points 89:circle 83:, the 65:  63:  53:  41:  39:  33:  2348:(PDF) 2333:S2CID 2205:(PDF) 2183:S2CID 2035:Notes 1970:when 1306:where 641:sides 103:are: 87:is a 2303:LCCN 2264:LCCN 1389:are 1374:The 1276:ABCD 581:ABCD 573:ABCD 562:ABCD 545:Let 326:The 269:and 156:), 116:foot 114:The 107:The 2462:at 2441:at 2432:at 2325:doi 2321:103 2175:doi 2171:103 2086:doi 2082:116 1997:ABC 1978:ABC 1954:ABC 1939:ABC 1888:sin 1870:sin 1852:sin 1825:sin 1800:sin 1775:sin 1695:sin 1679:cos 1649:sin 1633:cos 1603:sin 1587:cos 1403:are 1259:DAB 1257:, △ 1255:CDA 1253:, △ 1251:BCD 1249:, △ 1247:ABC 1224:of 1217:DAB 1215:, △ 1213:CDA 1211:, △ 1209:BCD 1207:, △ 1205:ABC 1024:As 587:EFG 568:EFG 234:). 148:), 79:In 2488:: 2418:. 2399:. 2356:, 2350:, 2331:, 2319:, 2301:, 2277:; 2262:, 2211:. 2207:. 2181:. 2169:. 2138:^ 2080:. 2076:. 2000:. 1903:0. 614:, 334:. 2424:. 2405:. 2358:7 2327:: 2289:. 2213:7 2189:. 2177:: 2133:. 2092:. 2088:: 1995:△ 1991:P 1976:△ 1972:P 1959:P 1952:△ 1948:P 1944:P 1937:△ 1900:= 1897:) 1894:C 1885:y 1882:x 1879:+ 1876:B 1867:x 1864:z 1861:+ 1858:A 1849:z 1846:y 1843:( 1840:2 1834:C 1831:2 1820:2 1816:z 1812:+ 1809:B 1806:2 1795:2 1791:y 1787:+ 1784:A 1781:2 1770:2 1766:x 1748:z 1744:y 1740:x 1719:) 1716:B 1710:A 1707:( 1699:2 1691:) 1688:C 1685:( 1676:: 1673:) 1670:A 1664:C 1661:( 1653:2 1645:) 1642:B 1639:( 1630:: 1627:) 1624:C 1618:B 1615:( 1607:2 1599:) 1596:A 1593:( 1553:c 1547:2 1543:) 1537:2 1533:b 1524:2 1520:a 1516:( 1510:: 1505:b 1499:2 1495:) 1489:2 1485:a 1476:2 1472:c 1468:( 1462:: 1457:a 1451:2 1447:) 1441:2 1437:c 1428:2 1424:b 1420:( 1393:. 1356:. 1347:M 1344:N 1338:2 1335:= 1326:N 1323:O 1304:M 1300:O 1296:N 1289:2 1286:/ 1283:1 1245:△ 1203:△ 1175:. 1170:2 1166:R 1162:4 1159:= 1154:2 1144:H 1141:P 1134:+ 1129:2 1119:C 1116:P 1109:+ 1104:2 1094:B 1091:P 1084:+ 1079:2 1069:A 1066:P 1046:P 1042:N 1038:K 1034:P 1030:N 1026:P 1012:. 1005:2 1001:R 997:3 989:2 985:K 976:2 973:1 960:N 956:P 952:K 932:, 927:2 923:K 919:= 914:2 904:H 901:P 894:+ 889:2 879:C 876:P 869:+ 864:2 854:B 851:P 844:+ 839:2 829:A 826:P 802:R 780:2 776:R 772:3 769:= 764:2 754:H 751:N 744:+ 739:2 729:C 726:N 719:+ 714:2 704:B 701:N 694:+ 689:2 679:A 676:N 656:P 652:N 590:. 585:△ 577:T 566:△ 547:ω 527:. 518:G 515:N 509:3 506:= 497:N 494:H 477:: 475:H 471:G 463:N 443:. 434:H 431:N 425:= 416:N 413:O 390:O 383:H 379:N 258:( 232:S 175:n 73:) 59:) 49:)

Index



Altitudes
orthocenter
circumcenter
nine-point center
geometry
circle
triangle
concyclic points
points
midpoint
foot
altitude
line segment
vertex
orthocenter
Karl Wilhelm Feuerbach
Leonhard Euler
Olry Terquem
nine-point center

vertex
acute triangle
obtuse triangle
Karl Wilhelm Feuerbach
Charles Brianchon
Jean-Victor Poncelet
Olry Terquem

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