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Find the derivative of f(x)=cos(2ln(-4x-3)).

Find the derivative of f(x)=cos(2ln(4x3))f(x)=\cos (2 \ln (-4 x-3)).

Full solution

Q. Find the derivative of f(x)=cos(2ln(4x3))f(x)=\cos (2 \ln (-4 x-3)).
  1. Identify Outer Function: Identify the outer function and its derivative.\newlineThe outer function is the cosine function, so we need to find the derivative of cos(u)\cos(u), where uu is a function of xx. The derivative of cos(u)\cos(u) with respect to uu is sin(u)-\sin(u).
  2. Identify Inner Function: Identify the inner function and its derivative.\newlineThe inner function is 2ln(4x3)2\ln(-4x-3). To find its derivative, we use the chain rule. The derivative of ln(v)\ln(v) with respect to vv is 1/v1/v, so the derivative of 2ln(v)2\ln(v) is 2/v2/v. Here, v=4x3v = -4x-3, so the derivative of the inner function is 2/(4x3)2/(-4x-3).
  3. Apply Chain Rule: Apply the chain rule.\newlineThe chain rule 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. So, we have:\newlinef(x)=sin(2ln(4x3))(ddx)(2ln(4x3))f'(x) = -\sin(2\ln(-4x-3)) \cdot \left(\frac{d}{dx}\right)(2\ln(-4x-3))
  4. Differentiate Inner Function: Differentiate the inner function.\newlineWe already found that the derivative of 2ln(4x3)2\ln(-4x-3) is 2(4x3)\frac{2}{(-4x-3)}. Now we need to differentiate 4x3-4x-3 with respect to xx, which is simply 4-4. So the derivative of the inner function is 2(4x3)×4\frac{2}{(-4x-3)} \times -4.
  5. Simplify Inner Function Derivative: Simplify the derivative of the inner function.\newlineMultiplying 2(4x3)\frac{2}{(-4x-3)} by 4-4 gives us 8(4x3)\frac{-8}{(-4x-3)}, which simplifies to 8(4x3)\frac{8}{(-4x-3)} because the negatives cancel out.
  6. Combine Derivatives: Combine the derivatives to find the final derivative.\newlineNow we multiply the derivative of the outer function by the simplified derivative of the inner function:\newlinef(x)=sin(2ln(4x3))(84x3)f'(x) = -\sin(2\ln(-4x-3)) \cdot \left(\frac{8}{-4x-3}\right)
  7. Simplify Final Expression: Simplify the final expression.\newlineWe can leave the final derivative in its current form, as it is already simplified:\newlinef(x)=8sin(2ln(4x3))/(4x3)f'(x) = -8\sin(2\ln(-4x-3))/(-4x-3)

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