Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 11: Parametric Equations and Polar Coordinates - Section 11.6 - Conic Sections - Exercises 11.6 - Page 678: 40

Answer

$ a.\qquad$ New vertex:$\quad V'(-1,3)$ New focus: $ \quad F'(-1,2)$ New directrix: $ \quad y=4$ $ b.\qquad$ See graph.

Work Step by Step

$ a.\qquad$ $x^{2}=-4y=-4(1)y$ Which has the form: $y=-\displaystyle \frac{x^{2}}{4p}$ ,$\qquad x^{2}=-4py\ \ $...opens down Vertex = $(0,0)$ Focus = $(0,-p)=(0,-1)$ Directrix: $y=p=1$ New vertex: $\left\{\begin{array}{ll} x'=x-1=0-1=-1 & \text{... shift left}\\ y'=y+3=0+3=3 & \text{... shift up} \end{array}\right., \quad V'(-1,3)$ New focus: $\left\{\begin{array}{ll} x'=x-1=0-1=-1 & \text{... shift left}\\ y'=y+3=-1+3=2 & \text{... shift up} \end{array}\right., \quad F'(-1,2)$ New directrix (horizontal line, shifted up): $y=4$ $ b.\qquad$ See graph. The vertex and focus are now on the line $x=-1$ (the y-axis is shifted left).
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