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Given the function \newlinef(x)=cos(4x),f(x)=\cos(4\sqrt{x}), find \newlinef(x).f^{\prime}(x).

Full solution

Q. Given the function \newlinef(x)=cos(4x),f(x)=\cos(4\sqrt{x}), find \newlinef(x).f^{\prime}(x).
  1. Identify Functions: We are given the function f(x)=cos(4x)f(x) = \cos(4\sqrt{x}) and we need to find its derivative f(x)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.
  2. Derivative of Outer Function: First, let's identify the outer function and the inner function. The outer function is cos(u)\cos(u), where u=4xu = 4\sqrt{x}, and the inner function is 4x4\sqrt{x}. We will need to take the derivative of both of these functions.
  3. Derivative of Inner Function: The derivative of the outer function cos(u)\cos(u) with respect to uu is sin(u)-\sin(u). We will later substitute uu with 4x4\sqrt{x}.
  4. Apply Chain Rule: The derivative of the inner function 4x4\sqrt{x} with respect to xx is 4×(1/2)×x(1/2)=2x(1/2)=2x4 \times (1/2) \times x^{(-1/2)} = 2x^{(-1/2)} = \frac{2}{\sqrt{x}}, using the power rule for derivatives.
  5. Simplify Final Answer: Now we apply the chain rule. The derivative of f(x)f(x) with respect to xx 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)×(2x)f'(x) = -\sin(4\sqrt{x}) \times \left(\frac{2}{\sqrt{x}}\right).
  6. Simplify Final Answer: Now we apply the chain rule. The derivative of f(x)f(x) with respect to xx 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)×(2x)f'(x) = -\sin(4\sqrt{x}) \times \left(\frac{2}{\sqrt{x}}\right). Simplify the expression for f(x)f'(x) to get the final answer. f(x)=2sin(4x)xf'(x) = -\frac{2\sin(4\sqrt{x})}{\sqrt{x}}.

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