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Find f(x)f'(x) where f(x)=3xcos(x)f(x)=3x\cos(x).

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Q. Find f(x)f'(x) where f(x)=3xcos(x)f(x)=3x\cos(x).
  1. Identify components: Identify the components of the function that will require the use of the product rule.\newlineThe function f(x)=3xcos(x)f(x) = 3x \cos(x) is a product of two functions, g(x)=3xg(x) = 3x and h(x)=cos(x)h(x) = \cos(x).
  2. Recall product rule: Recall the product rule for differentiation. The product rule states that the derivative of a product of two functions is the derivative of the first function times the second function plus the first function times the derivative of the second function. In formula terms, if f(x)=g(x)h(x)f(x) = g(x)h(x), then f(x)=g(x)h(x)+g(x)h(x)f'(x) = g'(x)h(x) + g(x)h'(x).
  3. Differentiate first function: Differentiate the first function g(x)=3xg(x) = 3x.\newlineThe derivative of g(x)g(x) with respect to xx is g(x)=ddx(3x)=3g'(x) = \frac{d}{dx}(3x) = 3.
  4. Differentiate second function: Differentiate the second function h(x)=cos(x)h(x) = \cos(x).\newlineThe derivative of h(x)h(x) with respect to xx is h(x)=ddx(cos(x))=sin(x)h'(x) = \frac{d}{dx}(\cos(x)) = -\sin(x).
  5. Apply product rule: Apply the product rule using the derivatives from steps 33 and 44.\newlineUsing the product rule, f(x)=g(x)h(x)+g(x)h(x)=3cos(x)+3x(sin(x))f'(x) = g'(x)h(x) + g(x)h'(x) = 3 \cdot \cos(x) + 3x \cdot (-\sin(x)).
  6. Simplify derivative: Simplify the expression for the derivative. f(x)=3cos(x)3xsin(x)f'(x) = 3\cos(x) - 3x\sin(x).

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