Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 11: Parametric Equations and Polar Coordinates - Section 11.6 - Conic Sections - Exercises 11.6 - Page 679: 52

Answer

$\displaystyle \frac{(x+4)^{2}}{16}+\frac{(y+5)^{2}}{25}=1$ New foci:$\quad (-4,-2)$ and $(-4,-8)$ New vertices:$\quad (-4,0)$ and $(-4, -10)$ New center:$\quad (-4,-5)$

Work Step by Step

Shift left by $4 \Rightarrow$ in the equation, replace $x$ with $x+4$ Shift down by $5 \Rightarrow$ in the equation, replace $y$ with $y+5$ New equation:$\displaystyle \quad \frac{(x+4)^{2}}{16}+\frac{(y+5)^{2}}{25}=1$ The ellipse $\displaystyle \frac{x^{2}}{16}+\frac{y^{2}}{25}=1$ has the form for which: Foci on the y-axis: $\quad \displaystyle \frac{x^{2}}{b^{2}}+\frac{y^{2}}{a^{2}}=1 \quad (a\gt b)$ $a=4,\quad b=5$ Center-to-focus distance: $c=\sqrt{a^{2}-b^{2}}=\sqrt{25-16}=3$ Foci:$\quad (0, \pm 3)$ Vertices:$\quad (0, \pm 5)$ Center:$\quad (0,0)$ The translations are such that $(x,y)\rightarrow(x',y')$, where $\left\{\begin{array}{ll} x'=x-4 & \text{... shift left}\\ y'=y-5 & \text{... shift down} \end{array}\right.$ New foci:$\quad (0-4, \pm 3-5)\Rightarrow\quad (-4,-2)$ and $(-4,-8)$ New vertices:$\quad (0-4, \pm 5-5)\Rightarrow\quad (-4,0)$ and $(-4, -10)$ New center:$\quad (0-4,-5+0)\quad =(-4,-5)$
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