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: 37

Answer

$(y+2)^{2}=-8(x+1)$ The latus rectum has endpoints $(-3,-6)$ and $(-3,2).$

Work Step by Step

1.$\quad $The directrix is vertical, so the parabola opens left or right. The focus and the vertex lie on a horizontal line, $y= -2.$ The focus is $4$ units left of the directrix, so it opens left. The vertex is halfway between the focus and directrix, $a=2$ units from either, $(h,k)=(-1,-2).$ 2.$\quad $ Using table 2: $\begin{array}{|c|c|c|c|} \hline {focus}&{directrix}&{equation}& ... opens\\ \hline {(h-a,k)}&{x=h+a}&{(y-k)^{2}=-4a(x-h)} &left\\ \hline \end{array}$ The equation is $(y+2)^{2}=-4(2)(x+1)$ that is, $\quad (y+2)^{2}=-8(x+1)$ 3.$\quad $For the latus rectum (line segment parallel to the directrix, containing the focus), set $x=-3$ $(y+2)^{2}=-8(-3+1)$ $(y+2)^{2}=16$ $y+2=\pm 4$ $y=-2\pm 4$ The latus rectum has endpoints $(-3,-6)$ and $(-3,2).$
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