Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 11 - Section 11.6 - Polar Equations of Conics - 11.6 Exercises - Page 830: 38

Answer

(a) $e=\frac{3}{5}$, directrix $y=-\frac{2}{3}$. (b) $r=\frac{1}{5-3sin(\theta-\frac{2\pi}{3})}$ (c) See graph.

Work Step by Step

The standard form of a conic polar equation is $r=\frac{ed}{1\pm e\cdot cos\theta}$ or $r=\frac{ed}{1\pm e\cdot sin\theta}$. The graph of the equation will be a parabola if $e=1$, an ellipse if $e\lt1$, and a hyperbola if $e\gt1$ (a) Rewrite the equation given in the Exercise as $r=\frac{2/5}{1-\frac{3}{5}sin\theta}$, we can identify that $e=\frac{3}{5}\lt1$ by comparing it with a standard equation above. Thus the graph of the equation will be an ellipse. With $ed=\frac{2}{5}$, we get $d=\frac{2}{3}$ and the directrix is given by $y=-d=-\frac{2}{3}$. (b) The equation after the rotation can be written as $r=\frac{1}{5-3sin(\theta-\frac{2\pi}{3})}$ (c) See graph.
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