Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 10 - Analytic Geometry - 10.2 The Parabola - 10.2 Assess Your Understanding - Page 648: 78

Answer

Vertex: $(0,0)$ Focus: $\left(0,-\dfrac{E}{4A}\right)$ Directrix: $y=\dfrac{E}{4A}$

Work Step by Step

We are given the equation: $Ax^2+Ey=0$, $A\not=0,E\not=0$ Rewrite the equation: $Ax^2=-Ey$ $x^2=-\dfrac{E}{A}y$ The equation is in the form: $(x-h)^2=4p(y-k)$ Therefore the equation is that of a parabola. Because the equation contains $x^2$, the parabola is vertical. Determine $h,k,p$: $h=0$ $k=0$ $4p=-\dfrac{E}{A}\Rightarrow p=-\dfrac{E}{4A}$ Determine the vertex: $(h,k)=(0,0)$ Determine the focus: $(h, k+p)=\left(0,0-\dfrac{E}{4A}\right)=\left(0,-\dfrac{E}{4A}\right)$ Determine the directrix: $y=h-a$ $y=0-\left(-\dfrac{E}{4A}\right)$ $y=\dfrac{E}{4A}$ We are given the equation: $Ax^2+Ey=0$, $A\not=0,E\not=0$ Rewrite the equation: $Ax^2=-Ey$ $x^2=-\dfrac{E}{A}y$ The equation is in the form: $(x-h)^2=4p(y-k)$ Therefore, the equation is that of a parabola. Because the equation contains $x^2$, the parabola is vertical, and its axis is vertical. Determine $h,k,p$: $h=0$ $k=0$ $4p=-\dfrac{E}{A}\Rightarrow p=-\dfrac{E}{4A}$ Determine the vertex: $(h,k)=(0,0)$ Determine the focus: $(h, k+p)=\left(0,0-\dfrac{E}{4A}\right)=\left(0,-\dfrac{E}{4A}\right)$ Determine the directrix: $y=h-a$ $y=0-\left(-\dfrac{E}{4A}\right)$ $y=\dfrac{E}{4A}$
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