turunan pertama fungsi f(x) = cos² (-3x-9) adalah f(x)=.....

f(x) = cos²(-3x-9)
misalkan :
u = -3x - 9
du/dx = -3
v = cos u
dv/du= -sin u
y = v²
dy/dv = 2v

dy/dx = dy/dv . dv/du . du/dx
= 2v . (-sin u) . (-3)
= 6cos u sin u
= 6 . (sin 2u)/2
= 3sin 2(-3x-9)