jika f(x) = sin x * cos 3x, maka f'(1/6 phi) =...

f(x) = sinx cos(3x) = (1/2)(sin4x - sin2x)
f'(x) = 2 cos4x - cos2x
dianggap Pi bukan Phi
f'(Pi/6) = 2cos(2Pi/3) - cos(Pi/3) = -3/2