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: 6

Answer

Focus is: $(-2,0)$ and directrix is: $x-2=0$ See the attached graph.
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Work Step by Step

Standard form of a parabola is given as: $y^2=4px$ ...(1) Formula to find focus is: $F(p,0)$ and formula to find directrix is: $x=-p$ or, $x+p=0$ As we are given that $y^2=-8x \\ or, y^2=4(-2)x$ Compare this form with the equation (1), we have: $p=-2$ Thus, Focus is: $(-2,0)$ and directrix is: $x-2=0$ See the attached graph.
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