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: 46

Answer

$(y-3)^{2}=-12(x-4)$ New focus: $\quad (1, 3)$ New directrix: $\quad x=7$ New vertex:$ \quad (4,3)$

Work Step by Step

Shift right by 4 $\Rightarrow$ in the equation, replace $x$ with $x-4$ Shift up by 3 $\Rightarrow$ in the equation, replace $y$ with $y-3$ New equation:$\quad (y-3)^{2}=-12(x-4)$ $y^{2}=-12x\quad $is of the form $y^{2}=-4px $ ,$\qquad x=\displaystyle \frac{y^{2}}{4p}$ ,$\qquad$ (opens left), $p=3$ focus: $\quad(-p,0)$= $\quad(-3,0)$ directrix: $ x=p\Rightarrow \quad x=3$ vertex:$\quad (0,0)$ The translations are such that $(x,y)\rightarrow(x',y')$, where $\left\{\begin{array}{ll} x'=x+4 & \text{... shift rightt}\\ y'=y+3 & \text{... shift up} \end{array}\right.$ New focus: $\quad(-3+4,0+3) = (1, 3)$ New directrix: $ x=3+4\Rightarrow \quad x=7$ New vertex:$\quad (0+4,0+4) = (4,3)$
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