University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 10 - Section 10.6 - Conics in Polar Coordinates - Exercises - Page 591: 37

Answer

Parabola, opens left, with directrix: $x=1.$

Work Step by Step

The polar equation for a conic with eccentricity $e$ is $r=\displaystyle \frac{ke}{1+e\cos\theta},$ where $x=k \gt 0$ is the vertical directrix, and $\left\{\begin{array}{ll} e=1 & \Rightarrow\text{parabola}\\ e \lt 1 & \Rightarrow\text{ellipse}\\ e \gt 1 & \Rightarrow\text{hyperbola} \end{array}\right.$ Here,$ \displaystyle \quad r=\frac{1\cdot 1}{1+1\cdot\cos\theta}$ $e=1 \Rightarrow$ this is a parabola $k=1, \Rightarrow$ directrix: $x=1$ (opens left, since the focus is at the origin) The vertex is at $\theta=0\quad $(the x-axis). Polar coordinates of the vertex: $(\displaystyle \frac{1}{1+1},0)=(\displaystyle \frac{1}{2},0)$
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