Find the arc length (s) of the curve r(t) = (4t + 2, −5t + 3, 2t - 5) for - 3 ≤ t ≤ 2

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...
Question

1.1.6

**Problem Statement**

Find the arc length (s) of the curve \(\vec{r}(t) = \langle 4t + 2, -5t + 3, -2t - 5 \rangle\) for \(-3 \leq t \leq 2\).

**Solution**

To find the arc length \(s\), evaluate the integral of the magnitude of the derivative of \(\vec{r}(t)\) with respect to \(t\) over the given interval. The formula for the arc length of a vector function is:

\[ s = \int_{a}^{b} \|\vec{r}'(t)\| \, dt \]

**Steps**

1. Calculate \(\vec{r}'(t)\) by differentiating each component:

   \[
   \vec{r}'(t) = \left\langle \frac{d}{dt}(4t + 2), \frac{d}{dt}(-5t + 3), \frac{d}{dt}(-2t - 5) \right\rangle = \langle 4, -5, -2 \rangle
   \]

2. Find the magnitude \(\|\vec{r}'(t)\|\):

   \[
   \|\vec{r}'(t)\| = \sqrt{4^2 + (-5)^2 + (-2)^2} = \sqrt{16 + 25 + 4} = \sqrt{45}
   \]

3. Integrate over the interval \([-3, 2]\):

   \[
   s = \int_{-3}^{2} \sqrt{45} \, dt = \sqrt{45} \cdot \int_{-3}^{2} \, dt = \sqrt{45} \cdot [t]_{-3}^{2}
   \]

4. Evaluate the integral:

   \[
   s = \sqrt{45} \cdot (2 - (-3)) = \sqrt{45} \cdot 5
   \]

5. Simplify the expression:

   \[
   s = 5\sqrt{45} = 15\sqrt{5}
   \]

Therefore, the arc length \(s\) is \(15\sqrt{5}\).
Transcribed Image Text:**Problem Statement** Find the arc length (s) of the curve \(\vec{r}(t) = \langle 4t + 2, -5t + 3, -2t - 5 \rangle\) for \(-3 \leq t \leq 2\). **Solution** To find the arc length \(s\), evaluate the integral of the magnitude of the derivative of \(\vec{r}(t)\) with respect to \(t\) over the given interval. The formula for the arc length of a vector function is: \[ s = \int_{a}^{b} \|\vec{r}'(t)\| \, dt \] **Steps** 1. Calculate \(\vec{r}'(t)\) by differentiating each component: \[ \vec{r}'(t) = \left\langle \frac{d}{dt}(4t + 2), \frac{d}{dt}(-5t + 3), \frac{d}{dt}(-2t - 5) \right\rangle = \langle 4, -5, -2 \rangle \] 2. Find the magnitude \(\|\vec{r}'(t)\|\): \[ \|\vec{r}'(t)\| = \sqrt{4^2 + (-5)^2 + (-2)^2} = \sqrt{16 + 25 + 4} = \sqrt{45} \] 3. Integrate over the interval \([-3, 2]\): \[ s = \int_{-3}^{2} \sqrt{45} \, dt = \sqrt{45} \cdot \int_{-3}^{2} \, dt = \sqrt{45} \cdot [t]_{-3}^{2} \] 4. Evaluate the integral: \[ s = \sqrt{45} \cdot (2 - (-3)) = \sqrt{45} \cdot 5 \] 5. Simplify the expression: \[ s = 5\sqrt{45} = 15\sqrt{5} \] Therefore, the arc length \(s\) is \(15\sqrt{5}\).
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