Find the derivative of f(x)

Question

Find f'(x) for f(x) = cos²(3x³).

Answer 1

Find f'(x) for f(x) = cos²(3x³).

Use the chain rule:

f' = 2*cos(3x³) *d/dx cos(3x³)

d/dx cos(3x³) = -sin(3x³)*9x²

So.....f' = 2*cos(3x³) * -sin(3x³)*9x²

CHECK this by graphing with a graphing calculator or online tool such as desmos.