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: 29

Answer

$x^2=\dfrac{4}{3}y$ Latus rectum points: $\left(-\dfrac{2}{3},\dfrac{1}{3}\right),\left(\dfrac{2}{3},\dfrac{1}{3}\right)$ See graph

Work Step by Step

We are given the parabola: Vertex: $(0,0)$ Axis of symmetry:: $x=0$ Point on the graph: $(2,3)$ Because the axis of symmetry is vertical, the parabola is vertical. Its standard equation is: $(x-h)^2=4p(y-k)$ Use the coordinates of the vertex to determine $h,k$: $(h,k)=(0,0)$ $h=0$ $k=0$ Determine $p$ using the point $(2,3)$: $(2-0)^2=4p(3-0)$ $4=12p$ $p=\dfrac{4}{12}=\dfrac{1}{3}$ Determine the parabola's equation: $x^2=4\left(\dfrac{1}{3}\right)y$ $x^2=\dfrac{4}{3}y$ The focus is: $(h,k+p)=\left(0,0+\dfrac{1}{3}\right)=\left(0,\dfrac{1}{3}\right)$ Determine the two points defining the latus rectum: $y=\dfrac{1}{3}$ $x^2=\dfrac{4}{3}\left(\dfrac{1}{3}\right)$ $x^2=\dfrac{4}{9}$ $x=\pm \dfrac{2}{3}$ $x=-\dfrac{2}{3}\Rightarrow x_1=-\dfrac{2}{3}$ $x=\dfrac{2}{3}\Rightarrow x_2=\dfrac{2}{3}$ $\Rightarrow \left(-\dfrac{2}{3},\dfrac{1}{3}\right),\left(\dfrac{2}{3},\dfrac{1}{3}\right)$ Plot the points and graph the parabola:
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