Theorem of the Day  

Theorems from Geometry and Trigonometry 

This is a subset of the complete theorem list for the convenience of those who are looking for a particular result in geometry or trigonometry.

Numbers in brackets are those from the complete listing.

1. Euler's Polyhedral Formula (26)
2. The Pythagorean Theorem (27)
3. Euler's Identity (36)
4. Girard's Theorem (37)
5. Pappus' Theorem (44)
6. Miquel's Triangle Theorem (55)
7. Morley's Miracle (56)
8. Thales' Theorem (63)
9. Brahmagupta's Formula (76)
10. Pick's Theorem (77)
11. The Delsarte–Goethals–Seidel Theorem (83)
12. The Five Circle Theorem (84)
13. The Rule of Sarrus (96)
14. The Happy Ending Problem (99)
15. Kepler's Conjecture (101)
16. Viète's Formula (102)
17. The Goins–Maddox–Rusin Theorem on Heron Triangles (104)
18. The Tverberg Partition Theorem (107)
19. The Analyst's Travelling Salesman Theorem (108)
20. Lambert's Formula (121)
21. A Theorem on Apollonian Circle Packings (130)
22. Theaetetus' Theorem on the Platonic Solids (132)
23. Euclid's Triangular Prism (149)
24. De Moivre's Theorem (152)
25. The Classification of Archimedean 4-Polytopes (160)
26. The Descartes Circle Theorem (179)
27. Archimedes' Equiareal Map Theorem (181)
28. Theorema Egregium (183)
29. al-Kāshi's Law of Cosines (188)
30. The Art Gallery Theorem (198)
31. Minkowski's Convex Body Theorem (200)
32. The Classification of the Semiregular Tilings (205)
33. Euler's Formula (206)
34. The 6-Circles Theorem (213)
35. The Pappus–Guldin Theorems (220)
36. The Spherical Law of Cosines (225)
37. Poncelet's Porism (229)
38. The Circle Area Theorem (233)
39. Euler's Product Formula for Sine (247)
40. The Power of a Point Theorem (250)
41. Dunn and Pretty's Triangle-Halving Deltoid (260)
42. Euclid's Pythagorean Formula (261)
43. The Shoelace Formula (263)
44. Wolstenholme's Inequality (270)
45. Cotes' Harmonic Means Theorem in Geometry (275)