Identify Functions: We are given the function f(x)=cos(4x) and we need to find its derivative f′(x). To do this, we will use the chain rule, which states that the derivative of a composite function is the derivative of the outer function evaluated at the inner function times the derivative of the inner function.
Derivative of Outer Function: First, let's identify the outer function and the inner function. The outer function is cos(u), where u=4x, and the inner function is 4x. We will need to take the derivative of both of these functions.
Derivative of Inner Function: The derivative of the outer function cos(u) with respect to u is −sin(u). We will later substitute u with 4x.
Apply Chain Rule: The derivative of the inner function 4x with respect to x is 4×(1/2)×x(−1/2)=2x(−1/2)=x2, using the power rule for derivatives.
Simplify Final Answer: Now we apply the chain rule. The derivative of f(x) with respect to x is the derivative of the outer function evaluated at the inner function times the derivative of the inner function. This gives us f′(x)=−sin(4x)×(x2).
Simplify Final Answer: Now we apply the chain rule. The derivative of f(x) with respect to x is the derivative of the outer function evaluated at the inner function times the derivative of the inner function. This gives us f′(x)=−sin(4x)×(x2). Simplify the expression for f′(x) to get the final answer. f′(x)=−x2sin(4x).
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