College Algebra (11th Edition)

Published by Pearson
ISBN 10: 0321671791
ISBN 13: 978-0-32167-179-0

Chapter 6 - Section 6.1 - Parabolas - 6.1 Exercises - Page 590: 24

Answer

Vertex = $(0,0)$; Focus = $\left(0, -\dfrac{9}{4}\right)$; Directrix $y=\dfrac{9}{4}$; Axis of symmetry $x=0$.

Work Step by Step

We are given that $x^2=-9y$ This equation has the form as $x^2 =4py$ wherein $4p=-9 \implies p=-\dfrac{9}{4}$ Here, the vertex is $(0,0)$ and the axis of symmetry is the $y$-axis, that is, $x=0$ and the $x$-term is squared which shows that the parabola is vertical with focus $(0,p)=\left(0, -\dfrac{9}{4}\right)$. Now, the directrix is $y=-p=-\left(-\dfrac{9}{4}\right)=\dfrac{9}{4}$ Our results are: Vertex = $(0,0)$; Focus = $\left(0, -\dfrac{9}{4}\right)$; Directrix $y=\dfrac{9}{4}$; Axis of symmetry $x=0$.
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