Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 10 - Parametric Equations and Polar Coordinates - 10.6 Exercises - Page 708: 16

Answer

(a) e = 6/5 (b) Hyperbola (c) y = -5/3 (d) Image below: --------------------

Work Step by Step

(a) $$r = \frac {10}{5 -6sin(\theta)} \div \frac{5}{5} = \frac {2}{1 - \frac 65 sin(\theta)}$$ Based on the original equation: $$\frac{ed}{1 - esin(\theta)}$$ $$e = 6/5$$ (b) $e = 6/5 $, therefore, this equation represents a hyperbola. (c) The equation has a $-sin (\theta)$ and the focus is at (0,0), thus, the equation of the directrix must be in the "$y = -c$" pattern. In this case: $c = d$: $$ed = 2 \longrightarrow d = \frac{2}{e} = \frac{2}{6/5} = 5/3 $$ $$y = -5/3$$ (d) Plot the points where $\theta = 0$, $\theta = \pi/2$, $\theta = \pi$ and $\theta = 3\pi/2$ $$r = \frac {10}{5 -6sin(0)} \longrightarrow (2, 0)$$ $$r = \frac {10}{5 -6sin(\pi/2)} \longrightarrow (-10, \pi/2)$$ $$r = \frac {10}{5 -6sin(\pi)} \longrightarrow (2, \pi)$$ $$r = \frac {10}{5 -6sin(3\pi/2)} \longrightarrow (10/11, 3\pi/2)$$ Draw a hyperbola that passes through these points.
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