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: 49

Answer

Vertex: $(0,2)$ Focus: $\left(-1,2\right)$ Directrix: $x=1$ See graph

Work Step by Step

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