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Circumconic and inconic

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A point in the interior of a triangle is the center of an inellipse of the triangle if and only if the point lies in the interior of the triangle whose vertices lie at the midpoints of the original triangle's sides. For a given point inside that
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of the one with greatest area coincides with the center of the ellipse. The given ellipse, going through this triangle's three vertices and centered at the triangle's centroid, is called the triangle's
2537: 711: 2302: 731: 1290: 1533: 200: 917: 1754: 1697: 1627: 318: 397: 1179: 256: 2097: 726: 1919: 2774: 1311: 429: 2488:{\displaystyle {\begin{aligned}L&=q_{1}r_{2}-r_{1}q_{2},\\M&=r_{1}p_{2}-p_{1}r_{2},\\N&=p_{1}q_{2}-q_{1}p_{2}.\end{aligned}}} 1767: 2654:
The lines connecting the tangency points of any inellipse of a triangle with the opposite vertices of the triangle are concurrent.
991: 2621:{\displaystyle {\frac {\text{Area of inellipse}}{\text{Area of triangle}}}=\pi {\sqrt {(1-2\alpha )(1-2\beta )(1-2\gamma )}},} 588: 1194: 1473: 2518: 17: 113: 851: 2698:, the unique ellipse that passes through a triangle's three vertices and is centered at the triangle's 1706: 1649: 1573: 264: 2871: 2517:. In general, the ratio of the inellipse's area to the triangle's area, in terms of the unit-sum 1635:
in which case it is tangent externally to one of the sides of the triangle and is tangent to the
355: 2713: 2717: 2695: 2275:{\displaystyle L^{4}x^{2}+M^{4}y^{2}+N^{4}z^{2}-2M^{2}N^{2}yz-2N^{2}L^{2}zx-2L^{2}M^{2}xy=0,} 1547: 1461: 1146: 980: 223: 213: 2707:, the unique conic which passes through a triangle's three vertices, its centroid, and its 8: 2731: 830:{\displaystyle {\begin{aligned}wv+vz&=0,\\uz+wx&=0,\\vx+uy&=0.\end{aligned}}} 409:
in 0,1, or 2 points according as the circumconic is an ellipse, parabola, or hyperbola.
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Conic section that passes through the vertices of a triangle or is tangent to its sides
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is a point on the general circumconic, then the line tangent to the conic at
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Weisstein, Eric W. "Circumconic." From MathWorld--A Wolfram Web Resource.
2751:, the unique circle that is internally tangent to a triangle's three sides 2735: 2708: 2734:, a rectangular hyperbola that passes through a triangle's orthocenter, 2513:, also called the midpoint inellipse, with its center at the triangle's 2807:
Weisstein, Eric W. "Inconic." From MathWorld--A Wolfram Web Resource.
1447:{\displaystyle u^{2}a^{2}+v^{2}b^{2}+w^{2}c^{2}-2vwbc-2wuca-2uvab=0,} 562:{\displaystyle u^{2}x^{2}+v^{2}y^{2}+w^{2}z^{2}-2vwyz-2wuzx-2uvxy=0.} 2764: 2748: 2699: 2668: 2514: 1561: 1542: 1299: 47: 2724:
and passing through the triangle's three vertices as well as its
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The lines tangent to the general inconic are the sidelines of
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which is maximized by the centroid's barycentric coordinates
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The lines tangent to the general circumconic at the vertices
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Chakerian, G. D. "A Distorted View of Geometry." Ch. 7 in
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fall on the line segment connecting the midpoints of the
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Each noncircular circumconic meets the circumcircle of
2540: 2300: 2100: 1922: 1770: 1709: 1652: 1576: 1476: 1314: 1197: 1149: 994: 854: 729: 706:{\displaystyle u(-au+bv+cw):v(au-bv+cw):w(au+bv-cw).} 591: 432: 358: 267: 226: 116: 1541:Of all triangles inscribed in a given ellipse, the 582:The center of the general circumconic is the point 2620: 2487: 2274: 2064: 1884: 1748: 1691: 1621: 1527: 1446: 1284: 1173: 1129: 911: 829: 705: 561: 391: 312: 250: 194: 2863: 2728:, orthocenter, and various other notable centers 2692:that passes through a triangle's three vertices 845:The center of the general inconic is the point 84:denotes not only the vertex but also the angle 2658: 2797:http://mathworld.wolfram.com/Circumconic.html 1285:{\displaystyle (vr+wq)x+(wp+ur)y+(uq+vp)z=0.} 572: 2828: 2826: 2824: 2822: 2820: 2818: 2816: 2509:The inellipse with the largest area is the 69:are distinct non-collinear points, and let 1528:{\displaystyle u\cos A+v\cos B+w\cos C=0.} 2809:http://mathworld.wolfram.com/Inconic.html 2663:All the centers of inellipses of a given 2813: 76:denote the triangle whose vertices are 14: 2864: 1298:The general circumconic reduces to a 416:is tangent to the three sidelines of 195:{\displaystyle a=|BC|,b=|CA|,c=|AB|,} 402:This line meets the circumcircle of 24: 912:{\displaystyle cv+bw:aw+cu:bu+av.} 25: 2883: 2843: 1749:{\displaystyle p_{2}:q_{2}:r_{2}} 1692:{\displaystyle p_{1}:q_{1}:r_{1}} 1637:extensions of the other two sides 1560:The general inconic reduces to a 953: 220:is the locus of a variable point 958: 2084:is the inconic, necessarily an 345:on the circumconic, other than 2801: 2789: 2610: 2595: 2592: 2577: 2574: 2559: 2050: 2020: 2008: 1978: 1966: 1936: 1876: 1847: 1841: 1812: 1806: 1777: 1622:{\displaystyle ubc+vca+wab=0,} 1270: 1252: 1243: 1225: 1216: 1198: 1124: 1106: 1103: 1085: 1079: 1061: 1058: 1040: 1034: 1016: 1013: 995: 697: 670: 661: 634: 625: 595: 577: 313:{\displaystyle uyz+vzx+wxy=0,} 185: 174: 160: 149: 135: 124: 80:. Following common practice, 42:that passes through the three 13: 1: 2782: 2528:of the inellipse's center, is 423:and is given by the equation 1758:are distinct points, and let 1554: 977:fourth point of intersection 7: 2674: 2659:Extension to quadrilaterals 392:{\displaystyle ux+vy+wz=0.} 10: 2888: 840: 2720:centered on a triangle's 929:, given by the equations 573:Centers and tangent lines 349:, is a point on the line 2519:barycentric coordinates 2088:, given by the equation 1174:{\displaystyle P=p:q:r} 258:satisfying an equation 251:{\displaystyle X=x:y:z} 58:in the sides, possibly 2671:of the quadrilateral. 2622: 2489: 2276: 2066: 1886: 1750: 1693: 1623: 1529: 1448: 1286: 1175: 1131: 971:in a point other than 913: 831: 707: 563: 393: 314: 252: 196: 2718:rectangular hyperbola 2696:Steiner circumellipse 2623: 2490: 2277: 2067: 1887: 1751: 1694: 1624: 1548:Steiner circumellipse 1530: 1462:rectangular hyperbola 1449: 1287: 1176: 1132: 981:trilinear coordinates 914: 832: 708: 564: 394: 315: 253: 214:trilinear coordinates 197: 2538: 2298: 2098: 1920: 1768: 1707: 1650: 1574: 1474: 1312: 1195: 1147: 992: 852: 727: 589: 430: 356: 265: 224: 114: 95:, and similarly for 2732:Feuerbach hyperbola 1902:ranges through the 975:, often called the 720:are, respectively, 218:general circumconic 202:the sidelengths of 54:is a conic section 2834:Mathematical Plums 2618: 2485: 2483: 2272: 2062: 1910:is a line. Define 1882: 1746: 1689: 1619: 1525: 1444: 1282: 1171: 1127: 909: 827: 825: 703: 559: 389: 339:isogonal conjugate 310: 248: 192: 32:Euclidean geometry 2761:Mandart inellipse 2755:Steiner inellipse 2722:nine-point circle 2705:Kiepert hyperbola 2613: 2549: 2548: 2545: 2544:Area of inellipse 2511:Steiner inellipse 1898:As the parameter 62:, of a triangle. 16:(Redirected from 2879: 2837: 2830: 2811: 2805: 2799: 2793: 2770:Kiepert parabola 2648: 2627: 2625: 2624: 2619: 2614: 2558: 2550: 2547:Area of triangle 2546: 2543: 2542: 2527: 2494: 2492: 2491: 2486: 2484: 2477: 2476: 2467: 2466: 2454: 2453: 2444: 2443: 2417: 2416: 2407: 2406: 2394: 2393: 2384: 2383: 2357: 2356: 2347: 2346: 2334: 2333: 2324: 2323: 2281: 2279: 2278: 2273: 2256: 2255: 2246: 2245: 2224: 2223: 2214: 2213: 2192: 2191: 2182: 2181: 2166: 2165: 2156: 2155: 2143: 2142: 2133: 2132: 2120: 2119: 2110: 2109: 2083: 2071: 2069: 2068: 2063: 2058: 2057: 2045: 2044: 2032: 2031: 2016: 2015: 2003: 2002: 1990: 1989: 1974: 1973: 1961: 1960: 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2539: 2536: 2535: 2521: 2504:medial triangle 2482: 2481: 2472: 2468: 2462: 2458: 2449: 2445: 2439: 2435: 2428: 2422: 2421: 2412: 2408: 2402: 2398: 2389: 2385: 2379: 2375: 2368: 2362: 2361: 2352: 2348: 2342: 2338: 2329: 2325: 2319: 2315: 2308: 2301: 2299: 2296: 2295: 2251: 2247: 2241: 2237: 2219: 2215: 2209: 2205: 2187: 2183: 2177: 2173: 2161: 2157: 2151: 2147: 2138: 2134: 2128: 2124: 2115: 2111: 2105: 2101: 2099: 2096: 2095: 2079: 2053: 2049: 2040: 2036: 2027: 2023: 2011: 2007: 1998: 1994: 1985: 1981: 1969: 1965: 1956: 1952: 1943: 1939: 1927: 1923: 1921: 1918: 1917: 1907: 1906:, the locus of 1899: 1867: 1863: 1854: 1850: 1832: 1828: 1819: 1815: 1797: 1793: 1784: 1780: 1769: 1766: 1765: 1740: 1736: 1727: 1723: 1714: 1710: 1708: 1705: 1704: 1702: 1683: 1679: 1670: 1666: 1657: 1653: 1651: 1648: 1647: 1645: 1575: 1572: 1571: 1557: 1475: 1472: 1471: 1375: 1371: 1365: 1361: 1352: 1348: 1342: 1338: 1329: 1325: 1319: 1315: 1313: 1310: 1309: 1196: 1193: 1192: 1182: 1148: 1145: 1144: 993: 990: 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point 321: 320: 309: 306: 303: 300: 297: 294: 291: 288: 285: 282: 279: 276: 273: 270: 247: 244: 241: 238: 235: 232: 229: 191: 187: 183: 180: 176: 172: 169: 166: 162: 158: 155: 151: 147: 144: 141: 137: 133: 130: 126: 122: 119: 26: 9: 6: 4: 3: 2: 2884: 2873: 2870: 2869: 2867: 2857: 2854: 2851: 2848: 2847: 2835: 2829: 2827: 2825: 2823: 2821: 2819: 2817: 2810: 2804: 2798: 2792: 2788: 2776: 2773: 2771: 2768: 2766: 2762: 2759: 2756: 2753: 2750: 2747: 2746: 2745: 2742: 2737: 2733: 2730: 2727: 2723: 2719: 2716:hyperbola, a 2715: 2712: 2710: 2706: 2703: 2701: 2697: 2694: 2691: 2688:, the unique 2687: 2684: 2683: 2682: 2679: 2678: 2672: 2670: 2666: 2665:quadrilateral 2653: 2652: 2646: 2642: 2638: 2633: 2632: 2615: 2607: 2604: 2601: 2598: 2589: 2586: 2583: 2580: 2571: 2568: 2565: 2562: 2554: 2551: 2534: 2533: 2532: 2531: 2525: 2520: 2516: 2512: 2508: 2505: 2500: 2499: 2478: 2473: 2469: 2463: 2459: 2455: 2450: 2446: 2440: 2436: 2432: 2430: 2425: 2418: 2413: 2409: 2403: 2399: 2395: 2390: 2386: 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1601: 1598: 1595: 1592: 1589: 1586: 1583: 1580: 1577: 1570: 1569: 1568: 1567: 1563: 1559: 1558: 1549: 1544: 1540: 1539: 1522: 1519: 1516: 1513: 1510: 1507: 1504: 1501: 1498: 1495: 1492: 1489: 1486: 1483: 1480: 1477: 1470: 1469: 1468: 1467: 1463: 1459: 1458: 1441: 1438: 1435: 1432: 1429: 1426: 1423: 1420: 1417: 1414: 1411: 1408: 1405: 1402: 1399: 1396: 1393: 1390: 1387: 1384: 1381: 1376: 1372: 1366: 1362: 1358: 1353: 1349: 1343: 1339: 1335: 1330: 1326: 1320: 1316: 1308: 1307: 1306: 1305: 1301: 1297: 1296: 1279: 1276: 1273: 1267: 1264: 1261: 1258: 1255: 1249: 1246: 1240: 1237: 1234: 1231: 1228: 1222: 1219: 1213: 1210: 1207: 1204: 1201: 1191: 1190: 1189: 1188: 1168: 1165: 1162: 1159: 1156: 1153: 1150: 1142: 1141: 1121: 1118: 1115: 1112: 1109: 1100: 1097: 1094: 1091: 1088: 1082: 1076: 1073: 1070: 1067: 1064: 1055: 1052: 1049: 1046: 1043: 1037: 1031: 1028: 1025: 1022: 1019: 1010: 1007: 1004: 1001: 998: 988: 987: 986: 985: 982: 978: 969: 963: 962: 951: 947: 940: 933: 927: 906: 903: 900: 897: 894: 891: 888: 885: 882: 879: 876: 873: 870: 867: 864: 861: 858: 855: 848: 847: 846: 820: 817: 815: 810: 807: 804: 801: 798: 791: 788: 785: 783: 778: 775: 772: 769: 766: 759: 756: 753: 751: 746: 743: 740: 737: 734: 723: 722: 721: 700: 694: 691: 688: 685: 682: 679: 676: 673: 667: 664: 658: 655: 652: 649: 646: 643: 640: 637: 631: 628: 622: 619: 616: 613: 610: 607: 604: 601: 598: 592: 585: 584: 583: 556: 553: 550: 547: 544: 541: 538: 535: 532: 529: 526: 523: 520: 517: 514: 511: 508: 505: 502: 499: 494: 490: 484: 480: 476: 471: 467: 461: 457: 453: 448: 444: 438: 434: 426: 425: 424: 421: 415: 410: 407: 386: 383: 380: 377: 374: 371: 368: 365: 362: 359: 352: 351: 350: 340: 335: 331: 327: 307: 304: 301: 298: 295: 292: 289: 286: 283: 280: 277: 274: 271: 268: 261: 260: 259: 245: 242: 239: 236: 233: 230: 227: 219: 215: 210: 207: 189: 181: 178: 170: 167: 164: 156: 153: 145: 142: 139: 131: 128: 120: 117: 108: 103:as angles in 89: 74: 63: 61: 57: 53: 49: 45: 41: 40:conic section 37: 33: 19: 18:Circumellipse 2858:at MathWorld 2852:at MathWorld 2833: 2803: 2791: 2775:Yff parabola 2743: 2726:circumcenter 2686:Circumcircle 2681:Circumconics 2680: 2662: 2644: 2640: 2636: 2523: 2080: 1904:real numbers 976: 967: 945: 938: 931: 925: 921: 844: 715: 581: 419: 413: 411: 405: 401: 333: 329: 325: 322: 217: 211: 205: 106: 87: 72: 64: 51: 35: 29: 2850:Circumconic 2736:Nagel point 2709:orthocenter 1185:is given by 979:, given by 959:Circumconic 578:Circumconic 36:circumconic 2783:References 91:at vertex 2765:excircles 2669:diagonals 2608:γ 2602:− 2590:β 2584:− 2572:α 2566:− 2555:π 2456:− 2396:− 2336:− 2232:− 2200:− 2168:− 1514:⁡ 1499:⁡ 1484:⁡ 1460:and to a 1418:− 1400:− 1382:− 1116:− 1095:− 1071:− 1050:− 1026:− 1005:− 689:− 644:− 599:− 536:− 518:− 500:− 56:inscribed 50:, and an 2866:Category 2749:Incircle 2744:Inconics 2700:centroid 2675:Examples 2515:centroid 1562:parabola 1543:centroid 1300:parabola 332: : 328: : 65:Suppose 60:extended 48:triangle 44:vertices 2856:Inconic 2714:Jeřábek 2524:α, β, γ 2086:ellipse 1756:⁠ 1703:⁠ 1699:⁠ 1646:⁠ 1555:Inconic 973:A, B, C 841:Inconic 718:A, B, C 347:A, B, C 337:. The 110:. Let 78:A, B, C 67:A, B, C 52:inconic 2690:circle 216:, the 2288:where 46:of a 38:is a 1701:and 412:The 99:and 34:, a 2647:= ⅓ 1511:cos 1496:cos 1481:cos 1143:If 968:ABC 948:= 0 941:= 0 934:= 0 926:ABC 420:ABC 406:ABC 212:In 206:ABC 107:ABC 88:BAC 73:ABC 30:In 2868:: 2815:^ 2643:= 2639:= 1523:0. 1280:0. 950:. 943:, 936:, 821:0. 557:0. 387:0. 209:. 2649:. 2645:γ 2641:β 2637:α 2616:, 2611:) 2605:2 2599:1 2596:( 2593:) 2587:2 2581:1 2578:( 2575:) 2569:2 2563:1 2560:( 2552:= 2526:) 2522:( 2479:. 2474:2 2470:p 2464:1 2460:q 2451:2 2447:q 2441:1 2437:p 2433:= 2426:N 2419:, 2414:2 2410:r 2404:1 2400:p 2391:2 2387:p 2381:1 2377:r 2373:= 2366:M 2359:, 2354:2 2350:q 2344:1 2340:r 2331:2 2327:r 2321:1 2317:q 2313:= 2306:L 2270:, 2267:0 2264:= 2261:y 2258:x 2253:2 2249:M 2243:2 2239:L 2235:2 2229:x 2226:z 2221:2 2217:L 2211:2 2207:N 2203:2 2197:z 2194:y 2189:2 2185:N 2179:2 2175:M 2171:2 2163:2 2159:z 2153:4 2149:N 2145:+ 2140:2 2136:y 2130:4 2126:M 2122:+ 2117:2 2113:x 2107:4 2103:L 2081:X 2060:. 2055:2 2051:) 2047:t 2042:2 2038:r 2034:+ 2029:1 2025:r 2021:( 2018:: 2013:2 2009:) 2005:t 2000:2 1996:q 1992:+ 1987:1 1983:q 1979:( 1976:: 1971:2 1967:) 1963:t 1958:2 1954:p 1950:+ 1945:1 1941:p 1937:( 1934:= 1929:2 1925:X 1908:X 1900:t 1880:. 1877:) 1874:t 1869:2 1865:r 1861:+ 1856:1 1852:r 1848:( 1845:: 1842:) 1839:t 1834:2 1830:q 1826:+ 1821:1 1817:q 1813:( 1810:: 1807:) 1804:t 1799:2 1795:p 1791:+ 1786:1 1782:p 1778:( 1775:= 1772:X 1742:2 1738:r 1734:: 1729:2 1725:q 1721:: 1716:2 1712:p 1685:1 1681:r 1677:: 1672:1 1668:q 1664:: 1659:1 1655:p 1639:. 1617:, 1614:0 1611:= 1608:b 1605:a 1602:w 1599:+ 1596:a 1593:c 1590:v 1587:+ 1584:c 1581:b 1578:u 1550:. 1520:= 1517:C 1508:w 1505:+ 1502:B 1493:v 1490:+ 1487:A 1478:u 1442:, 1439:0 1436:= 1433:b 1430:a 1427:v 1424:u 1421:2 1415:a 1412:c 1409:u 1406:w 1403:2 1397:c 1394:b 1391:w 1388:v 1385:2 1377:2 1373:c 1367:2 1363:w 1359:+ 1354:2 1350:b 1344:2 1340:v 1336:+ 1331:2 1327:a 1321:2 1317:u 1277:= 1274:z 1271:) 1268:p 1265:v 1262:+ 1259:q 1256:u 1253:( 1250:+ 1247:y 1244:) 1241:r 1238:u 1235:+ 1232:p 1229:w 1226:( 1223:+ 1220:x 1217:) 1214:q 1211:w 1208:+ 1205:r 1202:v 1199:( 1183:P 1169:r 1166:: 1163:q 1160:: 1157:p 1154:= 1151:P 1125:) 1122:z 1119:a 1113:x 1110:c 1107:( 1104:) 1101:y 1098:c 1092:z 1089:b 1086:( 1083:: 1080:) 1077:y 1074:c 1068:z 1065:b 1062:( 1059:) 1056:x 1053:b 1047:y 1044:a 1041:( 1038:: 1035:) 1032:x 1029:b 1023:y 1020:a 1017:( 1014:) 1011:z 1008:a 1002:x 999:c 996:( 966:△ 946:z 939:y 932:x 924:△ 907:. 904:v 901:a 898:+ 895:u 892:b 889:: 886:u 883:c 880:+ 877:w 874:a 871:: 868:w 865:b 862:+ 859:v 856:c 818:= 811:y 808:u 805:+ 802:x 799:v 792:, 789:0 786:= 779:x 776:w 773:+ 770:z 767:u 760:, 757:0 754:= 747:z 744:v 741:+ 738:v 735:w 701:. 698:) 695:w 692:c 686:v 683:b 680:+ 677:u 674:a 671:( 668:w 665:: 662:) 659:w 656:c 653:+ 650:v 647:b 641:u 638:a 635:( 632:v 629:: 626:) 623:w 620:c 617:+ 614:v 611:b 608:+ 605:u 602:a 596:( 593:u 554:= 551:y 548:x 545:v 542:u 539:2 533:x 530:z 527:u 524:w 521:2 515:z 512:y 509:w 506:v 503:2 495:2 491:z 485:2 481:w 477:+ 472:2 468:y 462:2 458:v 454:+ 449:2 445:x 439:2 435:u 418:△ 404:△ 384:= 381:z 378:w 375:+ 372:y 369:v 366:+ 363:x 360:u 343:X 334:w 330:v 326:u 308:, 305:0 302:= 299:y 296:x 293:w 290:+ 287:x 284:z 281:v 278:+ 275:z 272:y 269:u 246:z 243:: 240:y 237:: 234:x 231:= 228:X 204:△ 190:, 186:| 182:B 179:A 175:| 171:= 168:c 165:, 161:| 157:A 154:C 150:| 146:= 143:b 140:, 136:| 132:C 129:B 125:| 121:= 118:a 105:△ 101:C 97:B 93:A 86:∠ 82:A 71:△ 20:)

Index

Circumellipse
Euclidean geometry
conic section
vertices
triangle
inscribed
extended
trilinear coordinates
isogonal conjugate
trilinear coordinates
parabola
rectangular hyperbola
centroid
Steiner circumellipse
parabola
extensions of the other two sides
real numbers
ellipse
medial triangle
Steiner inellipse
centroid
barycentric coordinates
quadrilateral
diagonals
Circumcircle
circle
Steiner circumellipse
centroid
Kiepert hyperbola
orthocenter

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