Chapter 10: Problem 11
Sketch the graph of the given equation, indicating vertices, foci, and asymptotes (if it is a hyperbola). $$ \frac{-x^{2}}{9}+\frac{y^{2}}{4}=1 $$
Short Answer
Expert verified
It's a vertical hyperbola with vertices at (0, ±2), foci at (0, ±√13), and asymptotes y = ±(2/3)x.
Step by step solution
01
Identify the Type of Conic Section
The equation given is \(\frac{-x^{2}}{9} + \frac{y^{2}}{4} = 1\). It is structured as \(-\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1\), which represents a hyperbola.
02
Determine the Orientation of the Hyperbola
Since the positive term (\(y^2\)) is associated with the \(y\)-axis, the hyperbola is oriented vertically (opens upwards and downwards).
03
Find the Vertices
For the hyperbola \(\frac{-x^2}{a^2} + \frac{y^2}{b^2} = 1\), the vertices are located at \( (0, \pm b) \). Here, \(b^2 = 4\), thus \(b = 2\). Therefore, the vertices are at \((0, 2)\) and \((0, -2)\).
04
Find the Asymptotes
The equations of the asymptotes of a vertical hyperbola are given by \(y = \pm \frac{b}{a}x\). Here, \(a^2 = 9\) so \(a = 3\), and \(b = 2\). The slope \(\frac{b}{a} = \frac{2}{3}\). Thus, the asymptotes are \(y = \frac{2}{3}x\) and \(y = -\frac{2}{3}x\).
05
Find the Foci
The foci of a vertical hyperbola are located at \((0, \pm c)\), where \(c^2 = a^2 + b^2\). Substituting the values, \(c^2 = 9 + 4 = 13\), and thus, \(c = \sqrt{13}\). The foci are therefore at \((0, \sqrt{13})\) and \((0, -\sqrt{13})\).
06
Sketch the Graph
To sketch the graph: locate the center at the origin \((0, 0)\), plot the vertices at \((0, 2)\) and \((0, -2)\), draw the asymptotes through the origin with slopes \(\frac{2}{3}\) and \(-\frac{2}{3}\). Finally, sketch the hyperbola opening upwards and downwards between the asymptotes, passing through the vertices.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertices of Hyperbola
In a hyperbola, the vertices are pivotal for understanding its shape and orientation. The vertices represent the closest points of the hyperbola to its center. In the case of the equation \(-\frac{x^2}{9} + \frac{y^2}{4} = 1\), we follow the general form \(-\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1\). Here, since the positive term lies with \(y^2\), the hyperbola is vertical.
- Orientation: A vertical hyperbola opens up and down, with its vertices along the y-axis.
- Finding the Vertices: The formula for the vertices is \((0, \pm b)\). From the equation, we have \(b^2 = 4\), which means \(b = 2\). Thus, the vertices are located at coordinates \((0, 2)\) and \((0, -2)\).
Foci of Hyperbola
The foci are crucial in the hyperbola's definition and are used to describe its elongation. For a hyperbola, every point on its branches has a consistent distance difference to these two fixed points called foci.
- Finding the Foci: The foci are located off the center, extending along the axis of the hyperbola. For a vertical hyperbola, the foci formula is \((0, \pm c)\), where \(c\) is derived from \(c^2 = a^2 + b^2\).
- Calculating \(c\): Substitute the given values \(a^2 = 9\) and \(b^2 = 4\) into the formula, yielding \(c^2 = 13\). Therefore, \(c = \sqrt{13}\).
- Foci Coordinates: The points are \((0, \sqrt{13})\) and \((0, -\sqrt{13})\).
Asymptotes of Hyperbola
Asymptotes provide a foundation for sketching hyperbolas accurately, showing how the branches of the hyperbola extend infinitely without bound. These diagonal lines frame the hyperbola but are never touched by its branches.
- Role of Asymptotes: They represent the directions in which the hyperbola opens, extending indefinitely along these guidelines.
- Equation of Asymptotes: For a vertical hyperbola, the asymptotes are determined by the formula \(y = \pm \frac{b}{a}x\).
- Calculating the Slope: In the equation \(-\frac{x^2}{9} + \frac{y^2}{4} = 1\), we find \(a = 3\) and \(b = 2\). Therefore, \(\frac{b}{a} = \frac{2}{3}\). The asymptote equations are \(y = \frac{2}{3}x\) and \(y = -\frac{2}{3}x\).