3. Let R be the region bounded by y = ln x, the x-axis, and the line x = e. Find the volume of the solid of revolution obtained by revolving R about the x-axis. Be sure to sketch the closed region R and the resulting solid.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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3. Let \( R \) be the region bounded by \( y = \ln x \), the \( x \)-axis, and the line \( x = e \). Find the volume of the solid of revolution obtained by revolving \( R \) about the \( x \)-axis. Be sure to sketch the closed region \( R \) and the resulting solid.

**Explanation of the Problem:**

1. **Region \( R \):**
   - **Boundaries:**
     - The curve \( y = \ln x \).
     - The \( x \)-axis which is the line \( y = 0 \).
     - The vertical line \( x = e \).

2. **Solid of Revolution:**
   - The region \( R \) is revolved around the \( x \)-axis to form a solid.
   - The task is to find the volume of this solid.

3. **Sketching:**
   - **The Region:**
     - Plot \( y = \ln x \) from \( x = 1 \) to \( x = e \).
     - Mark the area under the curve down to the \( x \)-axis and up to \( x = e \).
   - **Resulting Solid:**
     - Visualize the rotation of this region 360 degrees around the \( x \)-axis, creating a three-dimensional shape.

**Mathematical Approach:**

- Use the disk method to calculate the volume:
  \[
  V = \pi \int_{1}^{e} (\ln x)^2 \, dx
  \]
- Evaluate the integral to find the exact volume of the solid.
Transcribed Image Text:3. Let \( R \) be the region bounded by \( y = \ln x \), the \( x \)-axis, and the line \( x = e \). Find the volume of the solid of revolution obtained by revolving \( R \) about the \( x \)-axis. Be sure to sketch the closed region \( R \) and the resulting solid. **Explanation of the Problem:** 1. **Region \( R \):** - **Boundaries:** - The curve \( y = \ln x \). - The \( x \)-axis which is the line \( y = 0 \). - The vertical line \( x = e \). 2. **Solid of Revolution:** - The region \( R \) is revolved around the \( x \)-axis to form a solid. - The task is to find the volume of this solid. 3. **Sketching:** - **The Region:** - Plot \( y = \ln x \) from \( x = 1 \) to \( x = e \). - Mark the area under the curve down to the \( x \)-axis and up to \( x = e \). - **Resulting Solid:** - Visualize the rotation of this region 360 degrees around the \( x \)-axis, creating a three-dimensional shape. **Mathematical Approach:** - Use the disk method to calculate the volume: \[ V = \pi \int_{1}^{e} (\ln x)^2 \, dx \] - Evaluate the integral to find the exact volume of the solid.
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