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: 35

Answer

$\quad (x+3)^{2}=4(y-3)$ The latus rectum has endpoints $(-1,4)$ and $(-5,4).$

Work Step by Step

1.$\quad $The axis of symmetry is perpendicular to the directrix (it is vertical). The vertical line through the focus is $x=-3.$ The focus is 2 units above the directrix $\quad \Rightarrow\quad $the parabola opens up. 2.$\quad $By 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 vertex is halfway between the focus and the directrix, one unit below the focus, one unit above the directrix so $(h,k)=( -3, 3).$ From the directrix $y=k-a=2,$ we find $a$ $3-a=2$ $a=1$ 3.$\quad $The equation of the parabola is $\quad (x+3)^{2}=4(1)(y-3)$ that is, $\quad (x+3)^{2}=4(y-3)$ 4.$\quad $For the latus rectum (line segment parallel to the directrix, containing the focus), set $y=4$ $(x+3)^{2}=4(4-3)$ $(x+3)^{2}=4$ $x+3=\pm 2$ $x=-3\pm 2$ The latus rectum has endpoints $(-1,4)$ and $(-5,4).$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.