Truman pertama f(x)= cos pangkat 3 x adalah...??

f(x) = cos³ x
f(x) = (cos x)³
.
u = cos x
du/dx  = - sin x

y = u³
dy/dx = 3u²

y' = dy/dx
y' = dy/du . du/dx
y' = 3u² . (-sin x)
y' = 3 cos² x (-sin x)
y' = - 3 cos² x sin x