1. Sin2x = 2Sinx·Cosx
2. Cos2x = 1-Sin²x
Cos2x = 2Cos²x-1
Cosx = 1-2Sin²x⁄2
Cosx = 2Cos²x⁄2-1
3. Sin²x = 1-Cos²x
4. Sin²x+Cos²x = 1
5. Tan²x = 1+Sec²x
6. 1+Tan²x = Sec²x
7. Cot²x = 1+Cosec²x
8. 2Sinx = (Sinx+Cosx)+(Sinx-Cosx)
9. 2Cosx = (Cosx-Sinx)+(Cosx+Sinx)
10. Sin3x = 3Sinx-4Sin³x
11. Cos3x = 4Cos³x- 3Cosx
12. Sin(x-y) = Sinx·Cosy-Cosx·Siny
13. Cos (x-y) = Cosx·Cosy+Sinx·Siny
14. Cos (x+y) = Cosx·Cosy-Sinx·Siny
15. Sin (π+x) = -Sinx
16. Cos (π+x) = -Cosx
17. Cos (π-x) = -Cosx
18. Tan (π+x) = Tanx
19. Tan (π-x) = -Tanx
20. Sin (2π+x) = Sinx
21. Sin (2π-x) = -Sinx
21. Cos(2π+x) = Cosx
21. Cos (2π-x) = Cosx
22. Tan (2π+x) = Tanx
23. Tan (2π-x) = – Tanx
Even and Odd Formulas
24. Sin(-x) = -Sinx
25. Cos(-x) = Cosx
26. Tan(-x) = -Tanx
27. Cosec(-x) = -Cosecx
29. Sec(-x) = Secx
30. Cot(-x) = -Cotx
Product to Sum Formulas
31. Sinx·Cosy = ½[Sin(A+B)+Sin(A-B)
32. Cosx·Cosy = ½[Cos(A+B+Cos(A-B)
33. Sinx·Siny = ½[Cos(A-B)-Cos(A+B)
34. Cosx·Siny = ½[Sin(x+y)-Sin(x-y)