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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 11.6.44a

Shifting Conic Sections


You may wish to review Section 1.2 before solving Exercises 39-56.


The hyperbola (y²/4) − (x²/5) = 1 is shifted 2 units down to generate the hyperbola (y + 2)²/4 − x²/5 = 1.
a. Find the center, foci, vertices, and asymptotes of the new hyperbola.

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Identify the original hyperbola equation: \(\frac{y^2}{4} - \frac{x^2}{5} = 1\). This is a vertical hyperbola centered at the origin \((0,0)\) because the \(y^2\) term is positive and comes first.
Recognize the shift applied: the hyperbola is shifted 2 units down, changing \(y\) to \(y + 2\). The new equation is \(\frac{(y + 2)^2}{4} - \frac{x^2}{5} = 1\). This means the center moves from \((0,0)\) to \((0, -2)\).
Find the center of the new hyperbola: since the shift is down by 2 units, the center is at \((0, -2)\).
Determine the vertices: for a vertical hyperbola of the form \(\frac{(y - k)^2}{a^2} - \frac{(x - h)^2}{b^2} = 1\), the vertices are located \(a\) units above and below the center. Here, \(a^2 = 4\), so \(a = 2\). Thus, vertices are at \((0, -2 + 2)\) and \((0, -2 - 2)\).
Find the foci: the distance \(c\) from the center satisfies \(c^2 = a^2 + b^2\). Given \(a^2 = 4\) and \(b^2 = 5\), calculate \(c = \sqrt{4 + 5}\). The foci are then at \((0, -2 + c)\) and \((0, -2 - c)\).
Write the equations of the asymptotes: for a vertical hyperbola centered at \((h,k)\), the asymptotes are given by \(y - k = \pm \frac{a}{b}(x - h)\). Substitute \(h=0\), \(k=-2\), \(a=2\), and \(b=\sqrt{5}\) to get the asymptote equations.

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Shifting Conic Sections

Shifting a conic section involves translating its graph horizontally or vertically without changing its shape. For a hyperbola, shifting the center from (h, k) to (h, k + c) modifies the equation by replacing y with (y - (k + c)) or x with (x - (h + c)). This translation affects the location of key features like the center, vertices, and foci but not their relative distances.
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Parabolas as Conic Sections

Properties of Hyperbolas

A hyperbola is defined by its center, vertices, foci, and asymptotes. The center is the midpoint between vertices; vertices lie along the transverse axis. The foci are points inside the hyperbola related to its eccentricity, and asymptotes are lines the hyperbola approaches at infinity. These features are derived from the standard form equation and parameters a, b, and c.
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Properties of Functions

Equations of Asymptotes for Hyperbolas

Asymptotes of a hyperbola are straight lines that the curve approaches but never touches. For a hyperbola centered at (h, k) with equation (y - k)²/a² - (x - h)²/b² = 1, the asymptotes have equations y - k = ±(a/b)(x - h). Understanding how to find and shift these lines is essential when the hyperbola is translated.
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Asymptotes of Hyperbolas