01. 1 + cot²θ = cos²θ
02. 1 + tan²θ = sec²θ
03. sin(A+B) = sinAcosB + cosAsinB
04. sin(A-B) = sinAcosB - cosAsinB
05. cos(A+B) = cosAcosB - sinAsinB
06. cos(A-B) = cosAcosB + sinAsinB
07. tan(A+B) = tanA + tanB / 1 - tanAtanB
08. tan(A-B) = tanA - tanB / 1 + tanAtanB
09. sin(A+B) + sin(A-B) = 2sinAcosB
10. sin(A+B) - sin(A-B) = 2cosASinB
11. cos(A+B) + cos(A-B) = 2cosAcosB
12. cos(A-B) - cos(A+B) = 2sinAsinB
13. sinC + sinD = 2 sin(C+D)/2 cos(C-D)/2
14. sinC - sinD = 2 cos(C+D)/2 sin(C-D)/2
15. cosC + cosD = 2 cos(C+D)/2 cos(C-D)/2
16. cosC - cosD = 2 sin(C+D)/2 sin(D-C)/2
17. 2sin²θ = 1 - cos2θ
18. 2cos²θ = 1 + cos2θ
19. sin2θ = 2 sinθ cosθ = 2tanθ / 1 + tan²θ
20. cos2θ = cos²θ - sin²θ = 1 - tan²θ / 1 + tan²θ
21. tan2θ = 2tanθ / 1 - tan²θ
22. sin3θ = 3sinθ - 4sin³θ
23. cos3θ = 4cos³θ - 3cosθ
24. tan3θ = 3tanθ - tan³θ / 1 - 3tan²θ
25. cot3θ = 3cotθ - cot3θ / 1 - 3cot2θ
26. sin(A+B)sin(A-B) = sin²A - sin²B = cos²B - cos²A
27. cos(A+B)cos(A-B) = cos²A - sin²B = cos²B - sin²A
28. tan(A+B)tan(A-B) = tan²A - tan²B / 1 - tanAtanB
