Compute the arc length function L = ||r'(u)|| du for r(t) = (9t2, 3t2, t), and a = 0.

Calculus: Early Transcendentals
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ISBN:9781285741550
Author:James Stewart
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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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### Arc Length Function Calculation

To compute the arc length function \( L \), we use the formula:

\[ L = \int_{a}^{t} \|r'(u)\| \, du \]

where \( r(t) = \begin{pmatrix} 9t^2 \\ 3t^2 \\ t^3 \end{pmatrix} \) and \( a = 0 \).

In this problem:
- \( r(t) \) is given as \( \begin{pmatrix} 9t^2 \\ 3t^2 \\ t^3 \end{pmatrix} \)
- The lower limit of the integral \( a \) is 0.

To find the arc length, we need to differentiate \( r(t) \) with respect to \( t \), find its magnitude \( \|r'(u)\| \), and then integrate.

The required steps are:

1. **Differentiate \( r(t) \)**:
   \[ r'(t) = \begin{pmatrix} \frac{d}{dt}(9t^2) \\ \frac{d}{dt}(3t^2) \\ \frac{d}{dt}(t^3) \end{pmatrix} = \begin{pmatrix} 18t \\ 6t \\ 3t^2 \end{pmatrix} \]

2. **Calculate the magnitude \( \|r'(u)\| \)**:
   \[
   \|r'(t)\| = \sqrt{(18t)^2 + (6t)^2 + (3t^2)^2} = \sqrt{324t^2 + 36t^2 + 9t^4} = \sqrt{360t^2 + 9t^4} = \sqrt{9t^2(40 + t^2)} \]
   \[
   = 3t\sqrt{40 + t^2}
   \]

3. **Integrate to find \( L \)**:
   \[
   L = \int_{0}^{t} 3u\sqrt{40 + u^2} \, du
   \]

This integral can be solved using a substitution method. Let \( u = \sqrt{40 + u^2} \Rightarrow du = u \, du\) within limits of integration from \( a = 0
Transcribed Image Text:### Arc Length Function Calculation To compute the arc length function \( L \), we use the formula: \[ L = \int_{a}^{t} \|r'(u)\| \, du \] where \( r(t) = \begin{pmatrix} 9t^2 \\ 3t^2 \\ t^3 \end{pmatrix} \) and \( a = 0 \). In this problem: - \( r(t) \) is given as \( \begin{pmatrix} 9t^2 \\ 3t^2 \\ t^3 \end{pmatrix} \) - The lower limit of the integral \( a \) is 0. To find the arc length, we need to differentiate \( r(t) \) with respect to \( t \), find its magnitude \( \|r'(u)\| \), and then integrate. The required steps are: 1. **Differentiate \( r(t) \)**: \[ r'(t) = \begin{pmatrix} \frac{d}{dt}(9t^2) \\ \frac{d}{dt}(3t^2) \\ \frac{d}{dt}(t^3) \end{pmatrix} = \begin{pmatrix} 18t \\ 6t \\ 3t^2 \end{pmatrix} \] 2. **Calculate the magnitude \( \|r'(u)\| \)**: \[ \|r'(t)\| = \sqrt{(18t)^2 + (6t)^2 + (3t^2)^2} = \sqrt{324t^2 + 36t^2 + 9t^4} = \sqrt{360t^2 + 9t^4} = \sqrt{9t^2(40 + t^2)} \] \[ = 3t\sqrt{40 + t^2} \] 3. **Integrate to find \( L \)**: \[ L = \int_{0}^{t} 3u\sqrt{40 + u^2} \, du \] This integral can be solved using a substitution method. Let \( u = \sqrt{40 + u^2} \Rightarrow du = u \, du\) within limits of integration from \( a = 0
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