Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 11 - Section 11.2 - Ellipses - 11.2 Exercises - Page 798: 67

Answer

$\frac{x^2}{1455642} +\frac{y^2}{1451610}=1$

Work Step by Step

Use the figure given in the Exercise. Step 1. Assume the orbit of Apollo 11.has a standard ellipse equation $\frac{x^2}{a^2} +\frac{y^2}{b^2}=1 $ with a center at the middle point between the Perilune and the Apolune. Step 2. Identify the given quantities: radius of the moon $r=1075mi$, the center of the moon is at one focus of the ellipse orbit. At Perilune, the distance to the moon center is $d_1=r+68=1143mi$. At Apolune, the distance to the moon center is $d_2=r+195=1270mi$. Step 3. The total distance $d_1+d_2=2a=2413$, thus $a=1206.5$. And for the moon center $c=a-d_1=63.5mi$ Step 4. Use the relationship $b^2=a^2-c^2$, we have $b^2=(1206.5)^2-(63.5)^2=1451610$ Step 5. Conclusion: the equation of the orbit can be written as $\frac{x^2}{1455642} +\frac{y^2}{1451610}=1$
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