Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 10 - Section 10.5 - Conic Sections - 10.5 Exercises - Page 709: 24

Answer

Foci: $(-1,2\pm\sqrt{13})$ Vertices: $(-1,0)$ and $(-1,4)$ Asymptotes: $y=-\frac{2}{3}x+\frac{4}{3}$ and $y=\frac{2}{3}x+\frac{8}{3}$

Work Step by Step

Recall: The hyperbola $\frac{(y-k)^2}{a^2}-\frac{(x-h)^2}{b^2}=1$ has the foci $(h, k\pm c)$ where $c^2=a^2+b^2$, the vertices $(h,k\pm a)$, and the asymptotes $y-k=\pm(a/b) (x-h)$. We have $9y^2-4x^2-36y-8x=4$. Rewrite this equation: $9y^2-36y-4x^2-8x=4$ $9y^2-36y+36-4x^2-8x-4=4+36-4$ $9(y-2)^2-4(x+1)^2=36$ $\frac{(y-2)^2}{4}-\frac{(x+1)^2}{9}=1$ Then, $h=-1$ $k=2$ $a^2=4\to a=2$ $b^2=9\to b=3$ $c=\sqrt{a^2+b^2}=\sqrt{4+9}=\sqrt{13}$ $a/b=2/3$ Find the foci: $(h,k\pm c)=(-1,2\pm \sqrt{13})$ Find the vertices: $(h,k\pm a)=(-1,2\pm 2)$ $(-1,0)$ or $(-1,4)$ Find the asymptotes: $y-k=\pm (a/b)(x-h)$ $y-2=\pm 2/3(x+1)$ $y=\pm 2/3(x+1)+2$ $y=-2/3(x+1)+2$ or $y=2/3(x+1)+2$ $y=-\frac{2}{3}x+\frac{4}{3}$ or $y=\frac{2}{3}x+\frac{8}{3}$
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