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: 35

Answer

$(x+3)^2=4(y-3)$ Latus rectum points: $(-5,4),(-1,4)$ See graph

Work Step by Step

We are given the parabola: Focus: $(-3,4)$ Directrix: $y=2$ 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 focus and the directrix to determine $h,k,p$: $(h,k+p)=(-3,4)$ $y=k-p=2$ $\begin{cases} h=-3\\ k+p=4\\ k-p=2 \end{cases}$ $\begin{cases} h=-3\\ k+p=4\\ k-p+k+p=2+4 \end{cases}$ $\begin{cases} h=-3\\ k+p=4\\ 2k=6 \end{cases}$ $\begin{cases} h=-3\\ k+p=4\\ k=3 \end{cases}$ $k+p=4$ $3+p=4$ $p=1$ Determine the parabola's equation: $(x+3)^2=4(1)(y-3)$ $(x+3)^2=4(y-3)$ Determine the two points defining the latus rectum: $y=4$ $(x+3)^2=4(4-3)$ $(x+3)^2=4$ $x+3=\pm 2$ $x+3=-2\Rightarrow x_1=-5$ $x+3=2\Rightarrow x_2=-1$ $\Rightarrow (-5,4),(-1,4)$ Plot the points and graph the parabola:
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