Найти производную функции f'(x)=(3-sin3x)*cos3x

F(x) = (3 - sin3x)cos3x
f'(x) = -3cos3x * cos3x - 3sin3x(3 - sin3x) =
       = -3 (cos3x)^2 - 9sin3x + 3(sin3x)^2 =
       = -3 + 3(sin3x)^2 + 3(sin3x)^2 - 9sin3x =
       = 6(sin3x)^2 - 9sin3x - 3