Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 10 - Analytic Geometry - 10.3 The Ellipse - 10.3 Assess Your Understanding - Page 657: 35

Answer

$\dfrac{x^2}{4}+\dfrac{y^2}{13}=1$ See graph

Work Step by Step

We are given the ellipse: Foci: $(0,-3),(0,3)$ $x$-intercepts: $-2,2$ Because the $x$-coordinates of the foci are the same, the ellipse has the equation: $\dfrac{(x-h)^2}{b^2}+\dfrac{(y-k)^2}{a^2}=1$ Determine $h,k,b$ using the $x$-intercepts: $(h-b,k)=(-2,0)\Rightarrow h-b=-2,k=0$ $(h+b,k)=(2,0)\Rightarrow h+b=2$ $k=0$ $\begin{cases} h-b=-2\\ h+b=2 \end{cases}$ $h-b+h+b=-2+2$ $2h=0$ $h=0$ $h+b=2$ $0+b=2$ $b=2$ Determine $c$ using the foci: $(h,k-c)=(0,-3)$ $(0,0-c)=(0,-3)$ $(0,-c)=(0,-3)$ $c=3$ Determine $a$: $a^2=b^2+c^2$ $a^2=2^2+3^2$ $a^2=13$ $a=\sqrt{13}$ The equation of the ellipse is: $\dfrac{x^2}{4}+\dfrac{y^2}{13}=1$ The center is: $(h,k)=(0,0)$ Graph the ellipse:
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