College Algebra (6th Edition)

Published by Pearson
ISBN 10: 0-32178-228-3
ISBN 13: 978-0-32178-228-1

Chapter 7 - Conic Sections - Exercise Set 7.1 - Page 671: 44

Answer

Foci: $(4, \sqrt{21})$ and $(4, -\sqrt{21})$.
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Work Step by Step

$\displaystyle \frac{(x-4)^{2}}{4}+\frac{(y-0)^{2}}{25}=1$ (major axis vertical), $a^{2}=25,$ $a=5$ $b^{2}=4$, $b=2$ Center: $(4, 0)$ $c^{2}=a^{2}-b^{2}=25-4=21,$ $c=\sqrt{21}\approx 4.583$ Foci are $c$ units above and $c$ units below the center. Foci: $(4, \sqrt{21})$ and $(4, -\sqrt{21})$.
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