Chapter 7: Problem 258
For the following exercises, determine the equation of the parabola using the information given. Focus (2,3) and directrix \(x=-2\)
Short Answer
Expert verified
The equation of the parabola is \(x^2 = 8y - 24\).
Step by step solution
01
Understand the Problem
We are given the focus of a parabola at (2,3) and a directrix of \(x=-2\). The parabola's equation can be derived using these elements as it opens horizontally due to the vertical directrix.
02
Use the Definition of a Parabola
A parabola is defined as the set of points equidistant from the focus and the directrix. So, we use the formula \((x-h)^2 = 4p(y-k)\) for a parabola with a horizontal orientation, where \((h,k)\) is the vertex, determined from the focus and directrix.
03
Find the Vertex
The vertex's x-coordinate lies midway between the x-coordinate of the focus and the directrix line. Since the directrix \(x=-2\) and the focus is at \(x=2\), the midpoint is \(x=0\). Thus, the vertex is \((0, 3)\).
04
Determine the Parameter p
The parameter \(p\) is the distance from the vertex to the focus along the x-axis. Since the focus is at \(x=2\) and the vertex at \(x=0\), \(p = 2\).
05
Write the Parabola Equation
Using the vertex \((0,3)\) and \(p=2\), we substitute into the standard equation \((x-h)^2=4p(y-k)\). Thus, \((x-0)^2=8(y-3)\) simplifies to \(x^2=8y-24\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Focus and Directrix
The focus and directrix are fundamental in understanding the geometry of a parabola. Think of the focus as a point and the directrix as a straight line that guide the shape of the parabola.
- The parabola is the set of all points that are equidistant from these two elements.
- If you take any point on the parabola, its distance to the focus is equal to its distance to the directrix.
Horizontal Parabola
A horizontal parabola opens to the left or right depending on the location of its focus and directrix.
- In this context, the focus is positioned along the horizontal axis from the directrix.
- Our example has a focus at \((2, 3)\) and a directrix at \(x = -2\), resulting in a horizontally opening parabola.
Vertex of a Parabola
The vertex is the turning point of the parabola and its coordinates are crucial in forming the equation.
- It lies exactly halfway between the focus and the directrix along the axis of symmetry of the parabola.
- In the problem provided, the vertex is calculated as halfway between the focus’s point on the x-axis and the directrix, giving us \((0,3)\).
Standard Form of Parabola
The standard form for a horizontal parabola's equation provides a systematic way to establish its shape and direction.
- The equation is structured as \((x-h)^2 = 4p(y-k)\), where \((h,k)\) is the vertex.
- In this equation, \(4p\) represents the distance between the vertex and the focus or the vertex and the directrix.