Precalculus: Mathematics for Calculus, 7th Edition

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

Chapter 11 - Section 11.4 - Shifted Conics - 11.4 Exercises - Page 814: 12

Answer

(a) Center: $C(3,-1)$ Vertices: $V_1(3,-7)$ and $V_2(3,5)$ Foci: $F_1(3,-1-4\sqrt 2)$ and $F_2(3,-1+4\sqrt 2)$ (b) Length of the major axis: $2a=12$ Length of the minor axis: $2b=4$ (c)

Work Step by Step

Equation of an ellipse with center at $(h,k)$ (major axis is vertical): $\frac{(x-h)^2}{b^2}+\frac{(y-k)^2}{a^2}=1$ $9x^2-54x+y^2+2y+46=0$ $9x^2-54x+81+y^2+2y+1=-46+81+1$ $9(x-3)^2+(y+1)^2=36$ $\frac{(x-3)^2}{4}+\frac{(y+1)^2}{36}=1$ $\frac{(x-3)^2}{2^2}+\frac{[y-(-1)]^2}{6^2}=1$ $h=3$ $k=-1$ Center: $C(3,-1)$ $a=6$ $b=2$ $c^2=a^2-b^2=36-4=32$ $c=4\sqrt 2$ The given equation can be obtained by shifting $\frac{x^2}{2^2}+\frac{y^2}{6^2}=1$ right 3 units and downward 1 unit. In this equation: Vertices: $V(0,±a)$ $V_1(0,-6)$ and $V_2(0,6)$ Foci: $F(0,±c)$ $F_1(0,-4\sqrt 2)$ and $F_2(0,4\sqrt 2)$ Now, shift these points 3 units to the right and 1 unit downward: Vertices: $V_1(3,-7)$ and $V_2(3,5)$ Foci: $F_1(3,-1-4\sqrt 2)$ and $F_2(3,-1+4\sqrt 2)$ Length of the major axis: $2a=12$ Length of the minor axis: $2b=4$
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