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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.PE.66

Graphing Conic Sections


Exercises 63-68 give equations for conic sections and tell how many units up or down and to the right or left each curve is to be shifted. Find an equation for the new conic section, and find the new foci, vertices, centers, and asymptotes, as appropriate. If the curve is a parabola, find the new directrix as well.


x²/169 + y²/144 = 1, right 5, up 12

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Identify the type of conic section given by the equation \(\frac{x^{2}}{169} + \frac{y^{2}}{144} = 1\). Since both \(x^{2}\) and \(y^{2}\) terms are positive and the equation equals 1, this is an ellipse centered at the origin \((0,0)\).
Recall the standard form of an ellipse centered at \((h,k)\): \(\frac{(x - h)^{2}}{a^{2}} + \frac{(y - k)^{2}}{b^{2}} = 1\). Here, \(a^{2} = 169\) and \(b^{2} = 144\), so \(a = 13\) and \(b = 12\).
Apply the given shifts: right 5 units and up 12 units. This changes the center from \((0,0)\) to \((5,12)\). Substitute \(h=5\) and \(k=12\) into the ellipse equation to get the new equation: \(\frac{(x - 5)^{2}}{169} + \frac{(y - 12)^{2}}{144} = 1\).
Find the new foci. For an ellipse, the focal distance \(c\) is given by \(c = \sqrt{a^{2} - b^{2}}\). Calculate \(c\) and then determine the coordinates of the foci relative to the new center \((5,12)\). Since \(a^{2} > b^{2}\), the major axis is along the x-axis, so the foci are at \((h \pm c, k)\).
Find the vertices. The vertices lie along the major axis at a distance \(a\) from the center. So, the vertices are at \((h \pm a, k)\). Since this is an ellipse, there are no asymptotes or directrix to find.

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Conic Sections and Their Standard Equations

Conic sections are curves obtained by intersecting a plane with a double-napped cone, including ellipses, parabolas, hyperbolas, and circles. Each has a standard equation form, such as the ellipse equation x²/a² + y²/b² = 1, where a and b determine the shape and size. Understanding these forms is essential for identifying the type of conic and its geometric properties.
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Parabolas as Conic Sections

Translation of Conic Sections

Translating a conic involves shifting its graph horizontally and/or vertically without changing its shape. This is done by replacing x with (x - h) and y with (y - k) in the equation, where h and k are the horizontal and vertical shifts, respectively. Translation affects the location of key features like centers, vertices, and foci.
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Parabolas as Conic Sections

Finding Key Features of Conics After Translation

Key features such as foci, vertices, centers, asymptotes, and directrices define the shape and position of conics. After translation, these points shift by the same amounts as the graph. Calculating their new coordinates requires adding the translation values to the original coordinates, ensuring an accurate description of the transformed conic.
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Geometries from Conic Sections
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Finding Parametric Equations and Tangent Lines


Find parametric equations for the given curve.


9x² + 4y² = 36

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Lines


Sketch the lines in Exercises 45–48 and find Cartesian equations for them.


r cos (θ + π/3) = 2

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Hyperbolas and Eccentricity


Exercises 25–28 give the eccentricities and the vertices or foci of hyperbolas centered at the origin of the xy-plane. In each case, find the hyperbola’s standard-form equation in Cartesian coordinates.


Eccentricity: 1.25

Foci: (0, ±5)

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Identifying Parametric Equations in the Plane


Exercises 1–6 give parametric equations and parameter intervals for the motion of a particle in the xy-plane. Identify the particle’s path by finding a Cartesian equation for it. Graph the Cartesian equation and indicate the direction of motion and the portion traced by the particle.


x = 4 cos t, y = 9 sin t, 0 ≤ t ≤ 2π

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Graphing Conic Sections


Find the eccentricities of the ellipses and hyperbolas in Exercises 59–62. Sketch each conic section. Include the foci, vertices, and asymptotes (as appropriate) in your sketch.


5y² − 4x² = 20

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Polar Coordinates


Exercises 19–22 give the eccentricities of conic sections with one focus at the origin of the polar coordinate plane, along with the directrix for that focus. Find a polar equation for each conic section.


e = 1/3, r sin θ = −6

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