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 797: 47

Answer

$\frac{x^2}{9} + \frac{y^2}{13} = 1$

Work Step by Step

RECALL: The standard equation of an ellipse with whose center is at (0, 0) is: (i) $\frac{x^2}{a^2} + \frac{y^2}{b^2}=1$ (horizontal major axis) (ii) $\frac{x^2}{b^2} + \frac{y^2}{a^2}=1$ (vertical major axis) where $a \gt b$ 2a = length of major axis 2b = length of minor axis c = distance of each focus from the center $a^2=b^2+c^2$ The foci are (0, -2) and (0, 2), which are equidistant from the origin (0, 0). This means that the ellipse has its center at (0, 0). The foci, when connect together, form a vertical segment. This means that the major axis is also vertical. The length of minor axis is 6 $\longrightarrow 2b=6 \longrightarrow b=3$ Each focus is 2 units away from the center so $c=2$. Solve for $b$ using the formula $a^2=b^2=c^2$ to have: $\\a^2 = b^2+c^2 \\a^2=3^2+2^2 \\a^2=9+4 \\a^2=13 \\a=\sqrt{13}$ Therefore, the equation of the ellipse is: $\\\frac{x^2}{b^2} + \frac{y^2}{a^2}=1 \\\frac{x^2}{3^2} + \frac{y^2}{(\sqrt{13})^2}=1 \\\frac{x^2}{9} + \frac{y^2}{13} = 1$
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