Math Problem Statement

Use logarithmic differentiation to find the derivative of the function y = (ln(x + 5))^x

Solution

The function presented is:

y=(ln(x+5))xy = \left(\ln(x + 5)\right)^x

We are asked to find the derivative of this function using logarithmic differentiation. Let's proceed step by step.

Steps for Logarithmic Differentiation:

  1. Take the natural logarithm of both sides:

    Apply ln\ln to both sides to simplify the product and exponent: lny=ln[(ln(x+5))x]\ln y = \ln\left[\left(\ln(x + 5)\right)^x\right]

  2. Use logarithm properties:

    We can bring the exponent xx down in front, applying the logarithmic property ln(ab)=bln(a)\ln(a^b) = b\ln(a): lny=xln(ln(x+5))\ln y = x \cdot \ln(\ln(x + 5))

  3. Differentiate both sides implicitly:

    • The left side, lny\ln y, differentiates to 1ydydx\frac{1}{y} \cdot \frac{dy}{dx}.
    • On the right side, we will need to apply the product rule. Let’s differentiate xln(ln(x+5))x \cdot \ln(\ln(x + 5)).

    Using the product rule for (x)(ln(ln(x+5)))(x) \cdot (\ln(\ln(x + 5))): [ \frac{d}{dx} \left[ x \cdot \ln(\ln(x + 5)) \right] = 1 \cdot \ln(\ln(x + 5)) + x \cdot \frac{d}{dx}\left[\ln(\ln(x + 5))\right] ]

    Now, for the derivative of ln(ln(x+5))\ln(\ln(x + 5)), use the chain rule: ddx[ln(ln(x+5))]=1ln(x+5)1x+5\frac{d}{dx} \left[\ln(\ln(x + 5))\right] = \frac{1}{\ln(x + 5)} \cdot \frac{1}{x + 5}

    So, the full derivative on the right-hand side becomes: ln(ln(x+5))+x1ln(x+5)1x+5\ln(\ln(x + 5)) + x \cdot \frac{1}{\ln(x + 5)} \cdot \frac{1}{x + 5}

  4. Solve for dydx\frac{dy}{dx}:

    Now, multiply both sides by yy to isolate dydx\frac{dy}{dx}: dydx=y[ln(ln(x+5))+xln(x+5)(x+5)]\frac{dy}{dx} = y \cdot \left[ \ln(\ln(x + 5)) + \frac{x}{\ln(x + 5)(x + 5)} \right]

  5. Substitute y=(ln(x+5))xy = (\ln(x + 5))^x:

    Since y=(ln(x+5))xy = (\ln(x + 5))^x, we can now substitute it back into the equation: dydx=(ln(x+5))x[ln(ln(x+5))+xln(x+5)(x+5)]\frac{dy}{dx} = (\ln(x + 5))^x \cdot \left[ \ln(\ln(x + 5)) + \frac{x}{\ln(x + 5)(x + 5)} \right]

This gives the derivative of the function y=(ln(x+5))xy = \left(\ln(x + 5)\right)^x using logarithmic differentiation.

Let me know if you'd like further details or clarification!

Here are 5 related questions for further exploration:

  1. How does logarithmic differentiation simplify taking derivatives of functions with variable exponents?
  2. What are other cases where logarithmic differentiation is useful?
  3. Can logarithmic differentiation be applied to trigonometric functions?
  4. How would you compute the second derivative of this function?
  5. What happens if we differentiate a logarithmic function with multiple variables?

Tip: Logarithmic differentiation is particularly useful when the function involves both products and powers, especially when the exponent itself is a function of xx.

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Math Problem Analysis

Mathematical Concepts

Logarithmic Differentiation
Chain Rule
Product Rule

Formulas

Logarithmic differentiation
Chain Rule: d/dx[f(g(x))] = f'(g(x)) * g'(x)
Product Rule: d/dx[u*v] = u'v + uv'

Theorems

Logarithmic differentiation properties
Derivative rules

Suitable Grade Level

University Level Calculus