I had trouble with these questions, some are probably easy but i can't do it.
Any help will be appreciated :)
These are questions are from 3unit fitzpatrick, exercises 21(c)
47. sin2x + sin4x + sin6x = 4cosxcos2xsin3x
49. sin^2(5x) - sin^(3x) = sin8xsin2x
51. cos35 + cos45 + cos75+ cos85 =...