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: 30

Answer

$y^2=\dfrac{9}{2}x$ Latus rectum points: $\left(\dfrac{9}{8},-\dfrac{9}{4}\right),\left(\dfrac{9}{8},\dfrac{9}{4}\right)$ See graph

Work Step by Step

We are given the parabola: Vertex: $(0,0)$ Axis of symmetry: $y=0$ Point on the graph: $(2,3)$ Because the axis of symmetry is horizontal, the parabola is horizontal. Its standard equation is: $(y-k)^2=4p(x-h)$ Use the coordinates of the vertex to determine $h,k$: $(h,k)=(0,0)$ $h=0$ $k=0$ Determine $p$ using the point $(2,3)$: $(3-0)^2=4p(2-0)$ $9=8p$ $p=\dfrac{9}{8}$ Determine the parabola's equation: $y^2=4\left(\dfrac{9}{8}\right)x$ $y^2=\dfrac{9}{2}x$ The focus is: $(h+p,k)=\left(0+\dfrac{9}{8},0\right)=\left(\dfrac{9}{8},0\right)$ Determine the two points defining the latus rectum: $x=\dfrac{9}{8}$ $y^2=\dfrac{9}{2}\left(\dfrac{9}{8}\right)$ $y^2=\dfrac{81}{16}$ $y=\pm \dfrac{9}{4}$ $y=-\dfrac{9}{4}\Rightarrow y_1=-\dfrac{9}{4}$ $y=\dfrac{9}{4}\Rightarrow y_2=\dfrac{9}{4}$ $\Rightarrow \left(\dfrac{9}{8},-\dfrac{9}{4}\right),\left(\dfrac{9}{8},\dfrac{9}{4}\right)$ Plot the points and graph the parabola:
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