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: 26

Answer

(a) Vertices: $V(0,±a)=V(0,±\frac{1}{2})$ Foci: $F(0,±c)=F(0,±\frac{\sqrt 5}{6})$ Eccentricity: $e=\frac{c}{a}=\frac{\frac{\sqrt 5}{6}}{\frac{1}{2}}=\frac{\sqrt 5}{3}$ (b) Length of the major axis: $2a=1$ Length of the minor axis: $2b=\frac{2}{3}$ (c)

Work Step by Step

$9x^2+4y^2=1$ $\frac{x^2}{\frac{1}{9}}+\frac{y^2}{\frac{1}{4}}=1$ $\frac{x^2}{(\frac{1}{3})^2}+\frac{y^2}{(\frac{1}{2})^2}=1$ The major axis is vertical. Equation of an ellipse when major axis is vertical (center at the origin): $\frac{x^2}{b^2}+\frac{y^2}{a^2}=1$ So: $a=\frac{1}{2}$ $b=\frac{1}{3}$ $c^2=a^2-b^2=\frac{1}{4}-\frac{1}{9}=\frac{5}{36}$ $c=\frac{\sqrt 5}{6}$ (a) Vertices: $V(0,±a)=V(0,±\frac{1}{2})$ Foci: $F(0,±c)=F(0,±\frac{\sqrt 5}{6})$ Eccentricity: $e=\frac{c}{a}=\frac{\frac{\sqrt 5}{6}}{\frac{1}{2}}=\frac{\sqrt 5}{3}$ (b) Length of the major axis: $2a=1$ Length of the minor axis: $2b=\frac{2}{3}$
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