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Ch. 11 - Parametric Equations and Polar Coordinates
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 11, Problema 11.7.20

Hyperbolas and Eccentricity


In Exercises 17-24, find the eccentricity of the hyperbola. Then find and graph the hyperbola's foci and directrices.


y² − x² = 4

Guida verificata passo dopo passo
1
Rewrite the given hyperbola equation \(y^{2} - x^{2} = 4\) in the standard form by dividing both sides by 4, resulting in \(\frac{y^{2}}{4} - \frac{x^{2}}{4} = 1\).
Identify the values of \(a^{2}\) and \(b^{2}\) from the standard form. Here, \(a^{2} = 4\) and \(b^{2} = 4\). Since the \(y^{2}\) term is positive and comes first, the hyperbola opens vertically.
Calculate \(c^{2}\) using the relationship for hyperbolas: \(c^{2} = a^{2} + b^{2}\). Substitute the values to get \(c^{2} = 4 + 4\).
Find the eccentricity \(e\) using the formula \(e = \frac{c}{a}\). Take the square root of \(c^{2}\) to find \(c\), then divide by \(a\) (which is the square root of \(a^{2}\)).
Determine the coordinates of the foci, which lie along the transverse axis (vertical axis here) at \((0, \pm c)\), and write the equations of the directrices, which are horizontal lines given by \(y = \pm \frac{a^{2}}{c}\).

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Standard Form of a Hyperbola

A hyperbola can be expressed in the standard form (y²/a²) - (x²/b²) = 1 or (x²/a²) - (y²/b²) = 1. This form helps identify the values of a² and b², which are essential for determining the hyperbola's shape, orientation, and key features like vertices and asymptotes.
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Circles in Standard Form Example 1

Eccentricity of a Hyperbola

Eccentricity (e) measures how 'stretched' a hyperbola is and is defined as e = c/a, where c² = a² + b². It is always greater than 1 for hyperbolas, indicating the distance of the foci from the center relative to the vertices.
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Asymptotes of Hyperbolas

Foci and Directrices of a Hyperbola

The foci are two fixed points located along the transverse axis, at a distance c from the center. The directrices are lines perpendicular to the transverse axis, located at a distance a/e from the center. Both are used to define and graph the hyperbola accurately.
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Foci and Vertices of Hyperbolas