Chapter 9: Problem 20
Use vertices and asymptotes to graph each hyperbola. Locate the foci and find the equations of the asymptotes. $$9 y^{2}-x^{2}=1$$
Short Answer
Expert verified
The foci of the hyperbola are at positions (0, \(\sqrt{10}\)) and (0, -\(\sqrt{10}\)) while the equations of its asymptotes are \(y = 3x\) and \(y = -3x\).
Step by step solution
01
Identify the form of the equation
The equation is in the form \(\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1\). This indicates a hyperbola with a vertical transverse axis. With the constant on the right side being 1, we can identify that a^2 = 9 and b^2 = 1, implying that a = 3 (the vertical semi-axis length) and b = 1 (the horizontal semi-axis length).
02
Determine the center, vertices, and foci
The center of the hyperbola is at the origin (0,0) because the equation does not involve shifts in the x or y dimension. The vertices are at a distance 'a' above and below the center on the transverse axis. Hence, the vertices are (0, 3) and (0, -3). The distance from the center to the foci is \(\sqrt{a^2 + b^2} = \sqrt{9 + 1} = \sqrt{10}\), so the foci are at (0, \(\sqrt{10}\)) and (0, -\(\sqrt{10}\))
03
Find the equations of the asymptotes
The asymptotes for a hyperbola with a vertical transverse axis have the equations \(y = ± \frac{a}{b}x\), here this is \[y = ± \frac{3}{1}x\]. So the equations of asymptotes are \(y = 3x\) and \(y = -3x\)
04
Graph the Hyperbola
First graph the center point at (0,0). Then, plot other significant points: the vertices at (0, 3) and (0, -3), and the foci at (0, \(\sqrt{10}\)) and (0, -\(\sqrt{10}\)). Next, draw dashed lines for the asymptotes using the equations \(y = 3x\) and \(y = -3x\). Finally, draw the curve of the hyperbola approaching but never intersecting these asymptotes.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertices
In a hyperbola, the vertices are critical points located at the ends of the transverse axis. For the hyperbola given by the equation \(9y^2 - x^2 = 1\), the identified form is \(\frac{y^2}{3^2} - \frac{x^2}{1^2} = 1\). This form indicates a vertical transverse axis.
- The vertices are at a distance \(a\) from the center along this axis.
- Since \(a = 3\), the vertices occur at \((0, 3)\) and \((0, -3)\).
Asymptotes
Asymptotes are lines that guide the direction of the hyperbola's branches. Although the hyperbola approaches these lines, it never crosses them.
For a vertical hyperbola like \(9y^2 - x^2 = 1\), the asymptotes will intersect at the center of the hyperbola and form diagonals of an imaginary rectangle centered there.
For a vertical hyperbola like \(9y^2 - x^2 = 1\), the asymptotes will intersect at the center of the hyperbola and form diagonals of an imaginary rectangle centered there.
- The slopes of the asymptotes for a vertical hyperbola are given by \(\pm \frac{a}{b}\).
- The calculation shows the asymptotes are given by \(y = \pm 3x\).
Foci
Along with the vertices, the foci are important components of a hyperbola. They are points that lie along the transverse axis, providing a focal point from which the shape is mathematically defined.
- For the hyperbola in question, the distance to the foci from the center is found using \(\sqrt{a^2 + b^2}\).
- Substituting \(a^2 = 9\) and \(b^2 = 1\), the focus distance is \(\sqrt{10}\).
- Thus, the foci for \(9y^2 - x^2 = 1\) are located at \((0, \sqrt{10})\) and \((0, -\sqrt{10})\).
Equations of the Asymptotes
The asymptotic lines of a hyperbola can be calculated from its equation and are essential for understanding its shape. These lines provide a framework for sketching the hyperbola’s curves accurately.
- The equations of the asymptotes for \(9y^2 - x^2 = 1\), given the vertical form, use \(y = \pm \frac{a}{b}x\).
- Here, \(\frac{a}{b} = \frac{3}{1}\), resulting in the equations \(y = 3x\) and \(y = -3x\).
Graphing a Hyperbola
When graphing a hyperbola, start by plotting its basic components: the center, vertices, and foci. These points anchor the diagram and help convey the hyperbola's overall shape.
This process ensures the hyperbola is accurately represented on the coordinate plane.
- Begin by marking the center, which for \(9y^2 - x^2 = 1\) is at (0, 0).
- Plot the vertices at \((0, 3)\) and \((0, -3)\).
- Next, place the foci at \((0, \sqrt{10})\) and \((0, -\sqrt{10})\).
This process ensures the hyperbola is accurately represented on the coordinate plane.