Let f(x)=tan^−1(cos(6x)) . Find f ′ (x)

Let f(x)=tan^−1(cos(6x)) . Find f ′ (x)

NOTE: eq is like f(x) = 1/tan(cos(6x))

y = cot(cos(6x))
dy/dx = -csc(cos(6x))^2 * -sin(6x) * 6

f'(x) = 6 * sin(6x) * csc(cos(6x))^2

y = 1/[tan(cos(6x))] = [cot(cos(6x))]
y' = 6sin(6x) csc^2(cos(6 x))