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: 42

Answer

vertex: $\quad (0,0) $ focus: $\quad (0,-1)$ directrix: $\quad y=1$

Work Step by Step

Comparing the form of the equation with table 2, $\quad \quad \quad x^{2}=-4y\quad $has the form $\begin{array}{|c|c|c|c|} \hline {focus}&{directrix}&{equation}& ... opens\\ \hline {(h,k-a)}&{y=k+a}&{(x-h)^{2}=-4a(y-k)}& down \\ \hline \end{array}$ $(x-0)^{2}=-4(1)(y-0)\quad \Rightarrow\quad h=0, k=0, a=1$ vertex: $\quad (0,0) $ focus: $\quad (h,k-a)=(0,0-1)=(0,-1)$ directrix: $\quad y=k+a\quad \Rightarrow\quad y=1$ To graph, find the endpoints of the latus rectum (line segment parallel to the directrix, containing the focus) by setting $y=-1$ $x^{2}=-4(-1)$ $x^{2}=4$ $x=\pm 2$ Endpoints of the latus rectum: $(-2,-1), (2,-1)$
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