Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 10 - Analytic Geometry - 10.1 Parabolas - 10.1 Exercises - Page 967: 25

Answer

$$\eqalign{ & {\text{focus: }}\left( {0, - \frac{1}{{16}}} \right) \cr & {\text{directrix: }}y = \frac{1}{{16}} \cr & {\text{axis of symmetry: }}x = 0 \cr} $$

Work Step by Step

$$\eqalign{ & y = - 4{x^2} \cr & - \frac{1}{4}y = {x^2} \cr & {x^2} = - \frac{1}{4}y \cr & {\text{This equation is written in the form }}{x^2} = 4py.{\text{ }} \cr & {\text{represents a parabola with Vertical Axis }} \cr & {\text{of Symmetry and Vertex }}\left( {0,{\text{ }}0} \right). \cr & \underbrace {{x^2} = - \frac{1}{4}y}_{{x^2} = 4py} \cr & - \frac{1}{4}y = 4py \cr & p = - \frac{1}{{16}} \cr & {\text{With focus}}\left( {0,p} \right){\text{ and directrix }}y = - p \cr & {\text{focus: }}\left( {0, - \frac{1}{{16}}} \right) \cr & {\text{directrix: }}y = \frac{1}{{16}} \cr & {\text{axis of symmetry: }}x = 0 \cr} $$
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