Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 10 - Conics, Parametric Equations, and Polar Coordinates - 10.1 Exercises - Page 692: 24

Answer

$$\eqalign{ & {\text{Center}}\left( {0,0} \right) \cr & {\text{Foci }}\left( { - 3\sqrt 2 ,0} \right){\text{ and }}\left( {3\sqrt 2 ,0} \right) \cr & {\text{Vertex }}\left( { - \sqrt {21} ,0} \right){\text{ and }}\left( {\sqrt {21} ,0} \right) \cr & {\text{Eccentricity }}\frac{{2\sqrt 7 }}{7} \cr} $$

Work Step by Step

$$\eqalign{ & 3{x^2} + 7{y^2} = 63 \cr & {\text{Divide both sides of the equation by }}63 \cr & \frac{{3{x^2}}}{{63}} + \frac{{7{y^2}}}{{63}} = \frac{{63}}{{63}} \cr & \frac{{{x^2}}}{{21}} + \frac{{{y^2}}}{9} = 1 \cr & {\text{The equation has the standard form }}\frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} = 1,{\text{ }}a > b \cr & \frac{{{x^2}}}{{\left( {\sqrt {21} } \right)}} + \frac{{{y^2}}}{{{{\left( 3 \right)}^2}}} = 1 \Rightarrow a = \sqrt {21} ,b = 3 \cr & c = \sqrt {{a^2} - {b^2}} = \sqrt {21 - 9} = 2\sqrt 3 \cr & {\text{With}} \cr & {\text{Vertex }}\left( { - a,0} \right){\text{ and }}\left( {a,0} \right) \cr & {\text{Vertex }}\left( { - \sqrt {21} ,0} \right){\text{ and }}\left( {\sqrt {21} ,0} \right) \cr & {\text{Center}}\left( {0,0} \right) \cr & {\text{Foci }}\left( { - c,0} \right){\text{ and }}\left( {c,0} \right) \cr & {\text{Foci }}\left( { - 3\sqrt 2 ,0} \right){\text{ and }}\left( {3\sqrt 2 ,0} \right) \cr & {\text{Eccentricity }}e = \frac{c}{a} = \frac{{2\sqrt 3 }}{{\sqrt {21} }} = \frac{{2\sqrt 7 }}{7} \cr & {\text{Graph:}} \cr} $$
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