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 11.7 - Conics in Polar Coordinates - Exercises 11.7 - Page 685: 8

Answer

$F(0,\pm 12)$ Eccentricity$:\qquad e =\displaystyle \frac{12}{13}$ Directrices$:\quad y=\displaystyle \pm\frac{169}{12}$ Graph:

Work Step by Step

Write in standard form. $169x^{2}+25y^{2}=4225\qquad /\div 4225$ $\displaystyle \frac{x^{2}}{25}+\frac{y^{2}}{169}=1,\qquad a=5,b=13$ The major axis is vertical. $c=\sqrt{a^{2}-b^{2}}=\sqrt{169-25}=12$ $F(0,\pm 12)$ Eccentricity$:\qquad e=\displaystyle \frac{c}{a}=\frac{12}{13}$ Directrices$:\quad y=0\displaystyle \pm\frac{a}{e}$ $y=\displaystyle \pm\frac{13}{(\frac{12}{13})}$ $y=\displaystyle \pm\frac{169}{12}$ $(y\approx 14.08)$
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