Find Sax ds, where C is the line segment in the plane joining (0,0) and (3, 4).

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
**Problem Statement:**

Find \(\int_C x \, ds\), where \(C\) is the line segment in the plane joining \((0, 0)\) and \((3, 4)\).

---

**Solution Explanation:**

To solve this line integral, we'll follow these steps:

1. **Parametrize the Line Segment:**
   - We need to find a parametrization for the line segment \(C\).
   - The line segment can be parametrized by \(\mathbf{r}(t) = (1-t)(0, 0) + t(3, 4)\) for \(t \in [0, 1]\).
   - This simplifies to \(\mathbf{r}(t) = (3t, 4t)\).

2. **Compute \(ds\):**
   - The differential arc length \(ds\) is given by \(|\mathbf{r}'(t)| \, dt\).
   - Calculate the derivative: \(\mathbf{r}'(t) = (3, 4)\).
   - The magnitude is \(|\mathbf{r}'(t)| = \sqrt{3^2 + 4^2} = 5\).
   - Thus, \(ds = 5 \, dt\).

3. **Express \(x\) in Terms of \(t\):**
   - From \(\mathbf{r}(t) = (3t, 4t)\), we have \(x = 3t\).

4. **Evaluate the Integral:**
   \[
   \int_C x \, ds = \int_0^1 3t \cdot 5 \, dt = 15 \int_0^1 t \, dt
   \]
   
   - Compute \(\int_0^1 t \, dt\):
     \[
     \int_0^1 t \, dt = \left[ \frac{t^2}{2} \right]_0^1 = \frac{1}{2}
     \]

   - Substitute back:
     \[
     15 \int_0^1 t \, dt = 15 \cdot \frac{1}{2} = \frac{15}{2} = 7.5
     \]

Thus, the value of the line integral is \(7.5\).
Transcribed Image Text:**Problem Statement:** Find \(\int_C x \, ds\), where \(C\) is the line segment in the plane joining \((0, 0)\) and \((3, 4)\). --- **Solution Explanation:** To solve this line integral, we'll follow these steps: 1. **Parametrize the Line Segment:** - We need to find a parametrization for the line segment \(C\). - The line segment can be parametrized by \(\mathbf{r}(t) = (1-t)(0, 0) + t(3, 4)\) for \(t \in [0, 1]\). - This simplifies to \(\mathbf{r}(t) = (3t, 4t)\). 2. **Compute \(ds\):** - The differential arc length \(ds\) is given by \(|\mathbf{r}'(t)| \, dt\). - Calculate the derivative: \(\mathbf{r}'(t) = (3, 4)\). - The magnitude is \(|\mathbf{r}'(t)| = \sqrt{3^2 + 4^2} = 5\). - Thus, \(ds = 5 \, dt\). 3. **Express \(x\) in Terms of \(t\):** - From \(\mathbf{r}(t) = (3t, 4t)\), we have \(x = 3t\). 4. **Evaluate the Integral:** \[ \int_C x \, ds = \int_0^1 3t \cdot 5 \, dt = 15 \int_0^1 t \, dt \] - Compute \(\int_0^1 t \, dt\): \[ \int_0^1 t \, dt = \left[ \frac{t^2}{2} \right]_0^1 = \frac{1}{2} \] - Substitute back: \[ 15 \int_0^1 t \, dt = 15 \cdot \frac{1}{2} = \frac{15}{2} = 7.5 \] Thus, the value of the line integral is \(7.5\).
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