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 11.1 - Parametrizations of Plane Curves - Exercises 11.1 - Page 647: 12

Answer

$y=\displaystyle \frac{2-x}{2x-1},\ \ x\displaystyle \lt \frac{1}{2}.$

Work Step by Step

From the parametric equation for x, x varies from $\displaystyle \frac{1}{2}$ (as t nears -1) to $-\infty $ (as t nears 1). So, $x\displaystyle \lt \frac{1}{2}.$ $x=\displaystyle \frac{t}{t-1}=\frac{t-1+1}{t-1}=1+\frac{1}{t-1}$ $x-1=\displaystyle \frac{1}{t-1}$ $t-1=\displaystyle \frac{1}{x-1}$ $t=\displaystyle \frac{1}{x-1}+1=\frac{1+x-1}{1-x}$ $t=\displaystyle \frac{x}{x-1}$ Substituting into the parametric equation for y, $y=\displaystyle \frac{\frac{x}{x-1}-2}{\frac{x}{x-1}+1}=\frac{\frac{x-2(x-1)}{x-1}}{\frac{x+x-1}{x-1}}=\frac{2-x}{2x-1}$ $ \fbox{$y=\displaystyle \frac{2-x}{2x-1},\ \ x\lt \frac{1}{2}$}.$ To graph, create a table using several values for t, and then calculate $(x(t), y(t)),$ plotting the points as you go. Join with a smooth curve, noting the direction in which $t$ increases.
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