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: 27

Answer

$x^2=2y$ Latus rectum points: $(-1,0.5),(1,0.5)$ See graph

Work Step by Step

We are given the parabola: Vertex: $(0,0)$ Directrix: $y=-0.5$ Because the directrix is in the form $y=a$, the parabola is vertical. Its standard equation is: $(x-h)^2=4p(y-k)$ Use the coordinates of the vertex to determine $h,k$: $(h,k)=(0,0)$ $h=0$ $k=0$ Use the equation of the directrix to determine $p$: $y=k-p=-0.5$ $0-p=-0.5$ $p=0.5$ Determine the parabola's equation: $(x-0)^2=4(0.5)(y-0)$ $x^2=2y$ The focus is: $(h,k+p)=(0,0+0.5)=(0,0.5)$ Determine the two points defining the latus rectum: $y=0.5$ $x^2=2(0.5)$ $x^2=1$ $x=\pm 1$ $x=-1\Rightarrow x_1=-1$ $x=1\Rightarrow x_2=1$ $\Rightarrow (-1,0.5),(1,0.5)$ Plot the points and graph the parabola:
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