Chapter 12: Problem 26
Find an equation for the hyperbola that has its center at the origin and satisfies the given conditions. $$ \text { foci } F(0,\pm 10), \quad \text { asymptotes } y=\pm \frac{1}{3} x $$
Short Answer
Expert verified
The equation of the hyperbola is \( \frac{y^2}{90} - \frac{x^2}{10} = 1 \).
Step by step solution
01
Understand the Structure of a Hyperbola
A hyperbola with a center at the origin is generally expressed in the form \( \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 \) or \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \). Since the foci are along the y-axis, the equation will be in the form \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \).
02
Identify the Distance to the Foci
The foci of this hyperbola are given as \( (0, \pm 10) \), which means the distance from the center to a focus is \( c = 10 \). This will be used to find \( b \).
03
Use the Asymptote Slope to Find \(a\) and \(b\)
The asymptotes of a hyperbola in the form \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \) have slopes \( \pm \frac{a}{b} \). Given \( y = \pm \frac{1}{3}x \), we have \( \frac{a}{b} = \frac{1}{3} \).
04
Use the Relationship between \(a\), \(b\), and \(c\)
For hyperbolas of the form \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \), the relationship \( c^2 = a^2 + b^2 \) holds. We know \( c = 10 \), and \( \frac{a}{b} = \frac{1}{3} \), thus \( a = \frac{b}{3} \).
05
Setup Equations to Solve for \(b\)
From \( \left( \frac{b}{3} \right)^2 + b^2 = 10^2 \), simplify to \( \frac{b^2}{9} + b^2 = 100 \). Combine like terms: \( \frac{10b^2}{9} = 100 \).
06
Solve for \(b\)
Solve \( \frac{10b^2}{9} = 100 \) by multiplying both sides by 9: \( 10b^2 = 900 \). Divide by 10 to get \( b^2 = 90 \). Therefore, \( b = \sqrt{90} \).
07
Calculate \(a\) from \(b\)
Using \( a = \frac{b}{3} \) and knowing \( b = \sqrt{90} \), calculate \( a^2 = \left( \frac{\sqrt{90}}{3} \right)^2 = \frac{90}{9} = 10 \), so \( a = \sqrt{10} \).
08
Write the Equation of the Hyperbola
The equation of the hyperbola is \( \frac{y^2}{90} - \frac{x^2}{10} = 1 \), using the values found for \( a^2 = 10 \) and \( b^2 = 90 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Foci of Hyperbola
The foci of a hyperbola are crucial points that help define its shape and orientation. For a hyperbola centered at the origin with its foci on the y-axis, the coordinates are given as
- \( F(0, \, \pm c) \)
- \( (0, \, \pm 10) \)
- \(c^2 = a^2 + b^2\)
Asymptotes of Hyperbola
Asymptotes are imaginary lines that the hyperbola approaches but never actually touches or intersects. They give a skeleton or guide for the hyperbola’s open ends. For hyperbolas in the form
- \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \)
- \( \pm \frac{a}{b} \)
- \( y = \pm \frac{1}{3}x \)
Center of Hyperbola
The center of a hyperbola is the central point from which the various parts of the hyperbola are equidistant. For hyperbolas centered at the origin, the equation takes a simplified form. In this case, the center coordinates are
- \((0, 0)\)
Hyperbola Properties
Hyperbolas are fascinating geometric structures characterized by two symmetric ‘branches’. They have several defining properties:
- Shape and Equation: Hyperbolas have two parts that open outward, depicted in equations like
- \( \frac{y^2}{b^2} - \frac{x^2}{a^2} = 1 \)
- Axes: A hyperbola’s transverse axis extends between the two branches.
- Vertices and Foci: The hyperbola’s branches contain points called vertices, and its foci are located along the transverse axis.
- Equation Elements: It derives its properties from components such as \( a, b, \) and \( c \), which allow calculation of distances between various pivotal elements like foci and vertices.