2. Find the vertex, focus, and directrix of the parabola. Then sketch the graph. (x − 3)² = 8(y + 1)

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question
**Problem 2**: Find the vertex, focus, and directrix of the parabola. Then sketch the graph.

Given equation:

\[
(x - 3)^2 = 8(y + 1)
\]

### Solution

To find the vertex, focus, and directrix of the parabola, we start with the given equation:

\[
(x - 3)^2 = 8(y + 1)
\]

This is in the form \((x - h)^2 = 4p(y - k)\), where \((h, k)\) is the vertex, and \(p\) is the distance from the vertex to the focus and directrix.

**1. Vertex**:  
The vertex \((h, k)\) is \((3, -1)\).

**2. Focus**:  
Since \(4p = 8\), we have \(p = 2\). The focus is located at \((h, k + p)\). Therefore, the focus is at \((3, 1)\).

**3. Directrix**:  
The directrix is the line \(y = k - p\). So, the directrix is \(y = -3\).

### Graph Explanation

- The vertex of the parabola is at the point \((3, -1)\).
- The parabola opens upwards because the coefficient of \((y + 1)\) is positive.
- The focus \((3, 1)\) is inside the parabola, 2 units above the vertex.
- The directrix \(y = -3\) is a horizontal line below the vertex, 2 units below it.

The sketch of the parabola will be symmetric about the vertical line \(x = 3\) and will pass through the focus and be equidistant from the directrix.
Transcribed Image Text:**Problem 2**: Find the vertex, focus, and directrix of the parabola. Then sketch the graph. Given equation: \[ (x - 3)^2 = 8(y + 1) \] ### Solution To find the vertex, focus, and directrix of the parabola, we start with the given equation: \[ (x - 3)^2 = 8(y + 1) \] This is in the form \((x - h)^2 = 4p(y - k)\), where \((h, k)\) is the vertex, and \(p\) is the distance from the vertex to the focus and directrix. **1. Vertex**: The vertex \((h, k)\) is \((3, -1)\). **2. Focus**: Since \(4p = 8\), we have \(p = 2\). The focus is located at \((h, k + p)\). Therefore, the focus is at \((3, 1)\). **3. Directrix**: The directrix is the line \(y = k - p\). So, the directrix is \(y = -3\). ### Graph Explanation - The vertex of the parabola is at the point \((3, -1)\). - The parabola opens upwards because the coefficient of \((y + 1)\) is positive. - The focus \((3, 1)\) is inside the parabola, 2 units above the vertex. - The directrix \(y = -3\) is a horizontal line below the vertex, 2 units below it. The sketch of the parabola will be symmetric about the vertical line \(x = 3\) and will pass through the focus and be equidistant from the directrix.
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