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 647: 53

Answer

Vertex: $(-1,-1)$ Focus: $\left(-0.75,-1\right)$ Directrix: $x=-1.25$ See graph

Work Step by Step

We are given the parabola: $y^2+2y-x=0$ Put the equation in standard form: $(y^2+2y+1)-1-x=0$ $(y+1)^2=x+1$ The standard equation is: $(y-k)^2=4p(x-h)$ Determine $h,k,p$: $h=-1$ $k=-1$ $4p=1\Rightarrow p=0.25$ Determine the vertex: $(h,k)=(-1,-1)$ Determine the focus: $(h+p,k)=\left(-1+0.25,-1\right)=\left(-0.75,-1\right)$ Determine the directrix: $x=h-p$ $x=-1-0.25$ $x=-1.25$ Determine the two points defining the latus rectum: $x=-0.75$ $(y+1)^2=-0.75+1$ $(y+1)^2=0.25$ $y+1=\pm 0.5$ $y+1=-0.5\Rightarrow y_1=-1.5$ $y+1=0.5\Rightarrow y_2=-0.5$ $\Rightarrow (-0.75,-1.5),(-0.75,-0.5)$ Plot the points, draw the directrix, and graph the parabola:
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