Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 11: Parametric Equations and Polar Coordinates - Section 11.6 - Conic Sections - Exercises 11.6 - Page 679: 61

Answer

This is an ellipse, with the main axis on the x-axis: the center is $(-2,0)$ the foci are $(-4,0)$ and $(0,0)$ the vertices are $(-2\pm\sqrt{5},0)$.

Work Step by Step

We group like terms $(x^{2}+4x)+5y^{2}=1$ We complete the square $(x^{2}+4x+4)+5y^{2}=1+4$ $(x+2)^{2}+5y^{2}=5$ Divide with 5 $\displaystyle \frac{(x+2)^{2}}{5}+y^{2}=1$ This has the form $\quad \quad \displaystyle \frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1 \quad (a\gt b)$ Foci on the x-axis$, a=\sqrt{5}, \quad b=1$ Center-to-focus distance: $\quad c=\sqrt{a^{2}-b^{2}}=\sqrt{5-1}=2$ Foci: $\quad(\pm 2, 0)$ Vertices: $\quad (\pm\sqrt{5}, 0)$ When $x$ is replaced with $(x+2)$, a shift to the left is made. $(x,y)\rightarrow(x-2,y)$ (No vertical shift $\Rightarrow$ the main axis remains on the x-axis.) The center shifts to $(0-2,0)=(-2,0)$ The foci shift to $(\pm 2-2, 0)\Rightarrow (-4,0)$ and $(0,0)$ The vertices shift to $(-2\pm\sqrt{5}, 0)$
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