Table of Content

1. Triangles. Theorems and problems about triangles.

2. Circles. Theorems and problems about circles.

3. Triangle Centers

4. Archimedes' Book of Lemmas

5. Quadrilaterals

6. Adams' Circle

7. First Ajima-Malfatti Point

8. Second Ajima-Malfatti Point

9. Apollonius' Tangency Problem for Three Circles Illustration with animation and sound.

10. The Bevan Point

11. Blanchet Theorem

12. Butterfly Theorem. See also: Butterfly Theorem Puzzle

13. Carnot's Theorem

14. Ceva's Theorem

15. Clifford's Circles Chain Theorems

16. Equal Incircles Theorem

17. Equilic Quadrilateral.

18. Euler and his beautiful and extraordinary formula that links the 5 fundamental constants e, i, Pi , 1 and 0, together!

19. Eyeball Theorem. Illustration

20. Gergonne Point Theorem

21. Heron's Formula. Key facts and a purely geometric step-by-step proof.

22. Johnson's Theorem

23. Kurschak's Tile & Theorem

24. Langley Problem: 20° Isosceles Triangle Adventitious angles.

25. Lemoine Theorem Animated Angle

26. Menelaus' Theorem

27. Miquel's Pentagram. Proof

28. Miquel's Pentagram. Dynamic Geometry Cabri, GSP, Cinderella, C.a.R.

29. Monge & d'Alembert Three Circles Theorem I - Dynamic Geometry Requires Java applet 1.3 or higher.

30. Monge & d'Alembert Three Circles Theorem II - Dynamic Geometry Requires Java applet 1.3 or higher.

31. Morley's Theorem

32. Napoleon's Theorem

33. Nagel Point Theorem. See also: Nagel Point Flowchart Proof, Nagel Point Puzzle.

34. Newton's Theorem: Newton's Line

35. Nine-Point Center, Nine-Point Circle, Euler Line

36. Parallelogram with Squares theorem.

37. Pascal's Mystic Hexagram Theorem Proof

38. Pentagons and Pentagrams. Menelaus and Collinearity

39. Platonic Solids. Interactive animation.

40. Poncelet's Theorem

41. Proposed Problems about congruence of line segments, angles, and triangles. Level: High School, SAT Prep, College geometry.

42. Ptolemy's Theorem.

43. Ptolemy's Extension Cyclic Quadrilateral: Ratio of the Diagonals.

44. Sangaku Problem

45. Sangaku Problem 2

46. Sangaku Problem 3

47. Sawayama -Thebault's theorem

48. Semiperimeter and excircles of a triangle

49. Semiperimeter and incircle of a triangle

50. Semiperimeter, incircle and excircles of a triangle

51. Seven Circles Theorem

52. Simson Line

53. Simson Line: Angle between two Simson lines

54. Steiner's Theorem

55. 100° Isosceles Triangle Problem

56. Taylor Circle

57. Three Circles Theorem

58. Three Tangent Circles Theorem

59. Triangles

60. Triangle with the bisectors of the exterior angles. Collinearity

61. Triangle & squares. 22 theorems, visual illustrations.

62. Triangle with Squares 0 Two squares.

63. Triangle with Squares 1 Two squares.

64. Triangle with Squares 2 Two squares.

65. Triangle with Squares 3 Three squares.

66. Triangle with Squares 4 Finsler-Hadwiger Theorem.

67. Triangle with Squares 5 Two squares, median and altitude.

68. Triangle with Squares 6 Four squares.

69. Triangle Centers

70. Van Aubel's Theorem Quadrilateral with Squares

71. Generalizing Van Aubel: Michael de Villiers' Theorems.

72. Varignon and Wittenbauer parallelograms

73. Adjacent Angles and Five Bisectors

74. Mind Map of How to Solve Problems
    George Pólya's 1945 book How to Solve It is a book describing methods of problem solving.