Question

What is f'(X) on the equation ?

Answer 1

$f(x) = cos^{4} (4 - 3x)$

(derivative of cos(x) is -sin(x))

$f(x) = (cos(4-3x))^{4}$             [cos²x is same as (cosx)²]

f'(x) = 4(cos(4-3x))³ (-sin(4-3x)) (-3)
f'(x) = -12 (cos(4-3x))³(-sin(4-3x))
f'(x) = 12 cos³(4-3x) sin(4-3x)

Thus, c is the correct answer.