Math Problem Statement

Let f(x) = x^√x. Find f'(9).

Solution

The problem you uploaded asks to find the derivative of the function:

f(x)=xxf(x) = x^{\sqrt{x}}

and evaluate it at x=9x = 9.

Step-by-step solution:

  1. Rewrite the function using logarithms: f(x)=xx=eln(xx)=exln(x)f(x) = x^{\sqrt{x}} = e^{\ln(x^{\sqrt{x}})} = e^{\sqrt{x} \ln(x)}

    So now we have f(x)=exln(x)f(x) = e^{\sqrt{x} \ln(x)}.

  2. Differentiate using the chain rule: Let u(x)=xln(x)u(x) = \sqrt{x} \ln(x), then f(x)=eu(x)f(x) = e^{u(x)}.

    The derivative of f(x)f(x) is: f(x)=eu(x)u(x)f'(x) = e^{u(x)} \cdot u'(x)

    Now, let's differentiate u(x)u(x): u(x)=xln(x)=x1/2ln(x)u(x) = \sqrt{x} \ln(x) = x^{1/2} \ln(x)

    To differentiate u(x)u(x), use the product rule: u(x)=ddx(x1/2ln(x))=(12x1/2ln(x))+(x1/21x)u'(x) = \frac{d}{dx}\left( x^{1/2} \ln(x) \right) = \left( \frac{1}{2}x^{-1/2} \ln(x) \right) + \left( x^{1/2} \cdot \frac{1}{x} \right) Simplifying: u(x)=12xln(x)+1xu'(x) = \frac{1}{2\sqrt{x}} \ln(x) + \frac{1}{\sqrt{x}}

  3. Substitute back into the derivative of f(x)f(x): f(x)=exln(x)(12xln(x)+1x)f'(x) = e^{\sqrt{x} \ln(x)} \cdot \left( \frac{1}{2\sqrt{x}} \ln(x) + \frac{1}{\sqrt{x}} \right)

  4. Evaluate at x=9x = 9: First, calculate the components at x=9x = 9: 9=3,ln(9)=2ln(3)\sqrt{9} = 3, \quad \ln(9) = 2 \ln(3) So: u(9)=32ln(3)=6ln(3)u(9) = 3 \cdot 2 \ln(3) = 6 \ln(3) eu(9)=e6ln(3)=36=729e^{u(9)} = e^{6 \ln(3)} = 3^6 = 729 Now, calculate u(9)u'(9): u(9)=162ln(3)+13=ln(3)3+13u'(9) = \frac{1}{6} \cdot 2 \ln(3) + \frac{1}{3} = \frac{\ln(3)}{3} + \frac{1}{3} Therefore: f(9)=729(ln(3)3+13)=729ln(3)+13f'(9) = 729 \left( \frac{\ln(3)}{3} + \frac{1}{3} \right) = 729 \cdot \frac{\ln(3) + 1}{3} Simplify: f(9)=243(ln(3)+1)f'(9) = 243 (\ln(3) + 1)

Final answer:

f(9)=243(ln(3)+1)f'(9) = 243 (\ln(3) + 1)

Would you like any further details or clarifications?

Follow-up questions:

  1. How does the product rule apply in this situation, and how does it simplify the derivative?
  2. What is the chain rule, and why is it used when differentiating exln(x)e^{\sqrt{x} \ln(x)}?
  3. Can you explain the logarithmic property ln(xa)=aln(x)\ln(x^{a}) = a \ln(x) and how it helps simplify the function?
  4. How can we generalize this approach for other exponentials of the form xg(x)x^{g(x)}?
  5. How does knowing the natural logarithm of common numbers like ln(3)\ln(3) aid in solving problems like this?

Tip:

Whenever you encounter functions with exponents involving variables, applying logarithmic differentiation often simplifies the process of finding the derivative.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Exponentials
Logarithmic Differentiation
Chain Rule
Product Rule

Formulas

f(x) = e^{u(x)}, where u(x) = √x * ln(x)
f'(x) = e^{u(x)} * u'(x)
u'(x) = (1/2√x)ln(x) + 1/√x

Theorems

Chain Rule
Product Rule

Suitable Grade Level

College-Level Calculus