18. Give a rough sketch of the solid that is enclosed by the paraboloids z = x² + y² and z = 18 - x² - y² and use your sketch to set up but DO NOT evaluate the triple that would represent the volume between the two curves.

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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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### Problem 18

**Task:**  
Provide a rough sketch of the solid enclosed by the paraboloids \( z = x^2 + y^2 \) and \( z = 18 - x^2 - y^2 \). Use the sketch to set up, but **DO NOT** evaluate, the triple integral that represents the volume between the two surfaces.

**Explanation:**

1. **Paraboloids Description:**
   - \( z = x^2 + y^2 \) describes an upward-opening paraboloid with its vertex at the origin \((0,0,0)\).
   - \( z = 18 - x^2 - y^2 \) describes a downward-opening paraboloid with its vertex at \((0,0,18)\).

2. **Intersection:**
   - To find where the two paraboloids intersect, set their equations equal: \( x^2 + y^2 = 18 - x^2 - y^2 \).
   - Simplifying gives \( 2x^2 + 2y^2 = 18 \), or \( x^2 + y^2 = 9 \). This describes a circle of radius 3 in the \( xy \)-plane.

3. **Sketch Guidance:**
   - **Top View:** Circle of radius 3 centered at the origin.
   - **Side View:** Visualize one paraboloid opening upwards and the other downwards, meeting at a circle in the \( xy \)-plane.
   
4. **Triple Integral Setup (without evaluation):**
   - The integral will be in the form of:
     \[
     \int \int \int_{E} \, dV
     \]
     where \( E \) is the region bounded by the two paraboloids.
   - Consider cylindrical coordinates (due to symmetry), with bounds for \( r \) from 0 to 3, \( \theta \) from 0 to \( 2\pi \), and \( z \) from \( r^2 \) to \( 18 - r^2 \).
Transcribed Image Text:### Problem 18 **Task:** Provide a rough sketch of the solid enclosed by the paraboloids \( z = x^2 + y^2 \) and \( z = 18 - x^2 - y^2 \). Use the sketch to set up, but **DO NOT** evaluate, the triple integral that represents the volume between the two surfaces. **Explanation:** 1. **Paraboloids Description:** - \( z = x^2 + y^2 \) describes an upward-opening paraboloid with its vertex at the origin \((0,0,0)\). - \( z = 18 - x^2 - y^2 \) describes a downward-opening paraboloid with its vertex at \((0,0,18)\). 2. **Intersection:** - To find where the two paraboloids intersect, set their equations equal: \( x^2 + y^2 = 18 - x^2 - y^2 \). - Simplifying gives \( 2x^2 + 2y^2 = 18 \), or \( x^2 + y^2 = 9 \). This describes a circle of radius 3 in the \( xy \)-plane. 3. **Sketch Guidance:** - **Top View:** Circle of radius 3 centered at the origin. - **Side View:** Visualize one paraboloid opening upwards and the other downwards, meeting at a circle in the \( xy \)-plane. 4. **Triple Integral Setup (without evaluation):** - The integral will be in the form of: \[ \int \int \int_{E} \, dV \] where \( E \) is the region bounded by the two paraboloids. - Consider cylindrical coordinates (due to symmetry), with bounds for \( r \) from 0 to 3, \( \theta \) from 0 to \( 2\pi \), and \( z \) from \( r^2 \) to \( 18 - r^2 \).
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