Chapter 7: Problem 23
In Problems \(21-44,\) find an equation of the hyperbola that satisfies the given conditions. Foci \((0,\pm 4),\) one vertex (0,-2)
Short Answer
Expert verified
The equation of the hyperbola is \(\frac{y^2}{4} - \frac{x^2}{12} = 1\).
Step by step solution
01
Identify the orientation of the hyperbola
Since the foci are given as \((0, \pm 4)\), the hyperbola is centered on the y-axis and is vertically oriented. This means the general equation for the hyperbola will be of the form \(\frac{(y-k)^2}{a^2} - \frac{(x-h)^2}{b^2} = 1\).
02
Determine the center of the hyperbola
The center \((h, k)\) of the hyperbola is at the midpoint of the segment defined by the foci \((0,4)\) and \((0,-4)\). Thus, the center is \((0,0)\).
03
Identify the length of the semi-major axis \(a\)
Given that one vertex is at \((0, -2)\), the distance from the center of the hyperbola \((0,0)\) to the vertex is the length of \(a\), which is 2. Thus, \(a = 2\).
04
Calculate the distance between the foci \(c\)
The distance from the center \((0,0)\) to the foci \((0, \pm 4)\) is 4. So \(c = 4\).
05
Use the relationship between \(a\), \(b\), and \(c\)
For a hyperbola, the relationship \(c^2 = a^2 + b^2\) holds true. Substituting the known values, we have \(4^2 = 2^2 + b^2\), which simplifies to \(16 = 4 + b^2\).
06
Solve for \(b^2\)
From the equation \(16 = 4 + b^2\), we solve for \(b^2\) by subtracting 4 from both sides: \(b^2 = 12\).
07
Write the equation of the hyperbola
Substitute the values of the center \((0,0)\), \(a^2 = 4\), and \(b^2 = 12\) into the general form of the hyperbola equation: \(\frac{y^2}{4} - \frac{x^2}{12} = 1\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Center of Hyperbola
The center of a hyperbola is the point around which the hyperbola is symmetrically organized. In our example, we are given foci at
- (0, 4) and (0, -4)
- (0, 0)
Semi-Major Axis
The semi-major axis of a hyperbola refers to the longest radius of an ellipse-like shape from its center to its vertex. In a vertically oriented hyperbola, this runs along the y-direction. In our specific problem, one vertex is at (0, -2). Since the hyperbola's center is at (0, 0), the vertical distance from the center to this vertex is 2. Hence, for this hyperbola, we set the semi-major axis
- a = 2
Distance Between the Foci
The distance between the foci of a hyperbola, symbolized as c, is significant as it determines the stretch of the hyperbola along its primary axis. For the given system, the foci are at
- (0, 4) and (0, -4)
- c = 4
Relationship Between a, b, and c
For hyperbolas, the values of \(a\), \(b\), and \(c\) are connected by the equation:\[c^2 = a^2 + b^2\]In our problem, we know
- a = 2
- c = 4
- b^2 = 12