College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 7 - Section 7.2 - The Parabola - 7.2 Assess Your Understanding - Page 515: 27

Answer

$x^{2}=2y$ The latus rectum has endpoints $(-1,\displaystyle \frac{1}{2})$ and $(1,\displaystyle \frac{1}{2}).$

Work Step by Step

1. The directrix is horizontal$\quad \Rightarrow\quad $the axis of symmetry is vertical. The vertex lies on the line $x=0$. So does the focus. 2.$\quad $The vertex $(0,0)$ is 0.5 units above the directrix, the parabola opens up. 3.$\quad $The focus is another 0.5 units above the vertex $F=(0,0.5),\quad a=0.5$ 4.$\quad $From Table 2, $\begin{array}{|c|c|c|c|} \hline {focus}&{directrix}&{equation}& ... opens\\ \hline {(h,k+a)}&{y=k-a}&{(x-h)^{2}=4a(y-k)}&up\\ \hline \end{array}$ The equation is $\quad (x-0)^{2}=4(0.5)(y-0)$ that is, $\quad x^{2}=2y$ 5. For $y=\displaystyle \frac{1}{2}, \quad x^{2}=1\quad \Rightarrow\quad x=\pm 1$ The latus rectum (line segment parallel to the directrix, containing the focus) has endpoints $(-1,0.5)$ and $(1,0.5)$ We have enough details for the graph.
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