Find f'(9) if f(x) = 7x² +6x + 2 √x f'(9)=

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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**Problem Statement**

Find \( f'(9) \) if \( f(x) = \frac{7x^2 + 6x + 2}{\sqrt{x}} \).

**Task**

Calculate the derivative of the function \( f(x) \) and evaluate it at \( x = 9 \).

**Steps to Solve**

1. **Rewrite the Function:**  
   Express the function in terms of exponents to simplify differentiation:
   \[
   f(x) = \frac{7x^2 + 6x + 2}{x^{1/2}} = (7x^2 + 6x + 2) \cdot x^{-1/2}
   \]

2. **Use the Product Rule:**  
   Recall the product rule: if \( u(x) \) and \( v(x) \) are functions, then
   \[
   (uv)' = u'v + uv'
   \]

   Assign:
   \[
   u(x) = 7x^2 + 6x + 2, \quad v(x) = x^{-1/2}
   \]

   Differentiate:
   \[
   u'(x) = 14x + 6, \quad v'(x) = -\frac{1}{2}x^{-3/2}
   \]

3. **Apply the Product Rule:**
   \[
   f'(x) = u'v + uv' = (14x + 6)x^{-1/2} + (7x^2 + 6x + 2)\left(-\frac{1}{2}x^{-3/2}\right)
   \]

4. **Simplify \( f'(x) \):**
   Calculate each term and simplify the expression:
   \[
   f'(x) = (14x + 6)x^{-1/2} - \frac{1}{2}(7x^2 + 6x + 2)x^{-3/2}
   \]

5. **Evaluate \( f'(9) \):**
   Substitute \( x = 9 \) into the derivative function to find \( f'(9) \).
Transcribed Image Text:**Problem Statement** Find \( f'(9) \) if \( f(x) = \frac{7x^2 + 6x + 2}{\sqrt{x}} \). **Task** Calculate the derivative of the function \( f(x) \) and evaluate it at \( x = 9 \). **Steps to Solve** 1. **Rewrite the Function:** Express the function in terms of exponents to simplify differentiation: \[ f(x) = \frac{7x^2 + 6x + 2}{x^{1/2}} = (7x^2 + 6x + 2) \cdot x^{-1/2} \] 2. **Use the Product Rule:** Recall the product rule: if \( u(x) \) and \( v(x) \) are functions, then \[ (uv)' = u'v + uv' \] Assign: \[ u(x) = 7x^2 + 6x + 2, \quad v(x) = x^{-1/2} \] Differentiate: \[ u'(x) = 14x + 6, \quad v'(x) = -\frac{1}{2}x^{-3/2} \] 3. **Apply the Product Rule:** \[ f'(x) = u'v + uv' = (14x + 6)x^{-1/2} + (7x^2 + 6x + 2)\left(-\frac{1}{2}x^{-3/2}\right) \] 4. **Simplify \( f'(x) \):** Calculate each term and simplify the expression: \[ f'(x) = (14x + 6)x^{-1/2} - \frac{1}{2}(7x^2 + 6x + 2)x^{-3/2} \] 5. **Evaluate \( f'(9) \):** Substitute \( x = 9 \) into the derivative function to find \( f'(9) \).
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ddx(xn)=nx(n-1) for any real n

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