College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 7 - Section 7.2 - The Parabola - 7.2 Assess Your Understanding - Page 515: 38

Answer

$(x+4)^{2}=12(y-1)$ The latus rectum has endpoints $(-10,4)$ and $(2,4).$

Work Step by Step

1.$\quad $The directrix is horizontal, so the parabola opens up or down. The focus and the vertex lie on a verticall line, $x=-4.$ The focus is $6$ units above the directrix, so it opens up. The vertex is halfway between the focus and directrix, $a=3$ units from either, $(h,k)=(-4,1).$ 2.$\quad $ Using table 2: $\begin{array}{|c|c|c|c|} \hline {focus}&{directrix}&{equation}& ... opens\\ \hline {(h,k+a)}&{y=k-a}&{(x-h)^{2}=4a(y-k)}&up\\ \hline \end{array}$ The equation is $(x+4)^{2}=4(3)(y-1)$ that is, $\quad (x+4)^{2}=12(y-1)$ 3.$\quad $For the latus rectum (line segment parallel to the directrix, containing the focus), set $ y=4$ $(x+4)^{2}=12(4-1)$ $(x+4)^{2}=36$ $x+4=\pm 6$ $x=-4\pm 6$ The latus rectum has endpoints $(-10,4)$ and $(2,4).$
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