Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 9 - Section 9.3 - The Parabola - Exercise Set - Page 996: 3


Focus is: $(0,-1)$ and directrix is: $y=1$; $\bf{Graph (b)}$

Work Step by Step

Standard form of a parabola is given as: $x^2=4py$ ...(1) Formula to find focus is: $F(0,p)$ and formula to find directrix is: $y=-p$ As we are given that $x^2=-4y$ Compare this form with the equation (1), we have: $p=-1$ Thus, Focus is: $(0,-1)$ and directrix is: $y=1$ All the above information matches to the $\bf{Graph (b)}$
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