What is f'(x) if f(x)=cos(5x^4) f'(x)=-sin(20x^3) f'(x)=20x^3sin(5x^4) f'(x)=sin(20x^3)

To find the derivative of the function , we need to use the chain rule.The chain rule states that if and , then .In this case, let . Then .Now, we can find the derivatives: Using the chain rule, we have: Therefore, the correct answer is .