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 - 10.1 Exercises - Page 666: 20

Answer

The particle moves clockwise along an ellipse from (0,5) to (-2, 4). The equation of this ellipse is $\frac{1}{4}x^2 + (y-4)^2 = 1$

Work Step by Step

1. Convert the equation to a Cartesian one, so we can identify the type of curve: $x = 2sin (t)$ $x^2 = 4sin^2(t)$ $\frac{1}{4}x^2 = sin^2(t)$ $y = 4 + cos (t)$ $y - 4 = cos(t)$ $(y-4)^2 = cos^2(t)$ Adding the equations: $\frac{1}{4}x^2 + (y-4)^2 = sin^2(t) + cos^2(t)$ $\frac{1}{4}x^2 + (y-4)^2 = 1$ - As we can see by the equation, this curve is an ellipse with a radius of $\sqrt 4 = 2$ parallel to the x-axis, and a radius of $1$ along the y-axis. And with its center at $(0,4)$ 2. Find the initial and final point: Initial point: $t = 0$ $ x = 2 sin(0) = 2 (0) = 0$ $y = 4 + cos(0) = 4 + 1 = 5$ Final point: $t = \frac {3\pi} 2$ $ x = 2 sin(\frac {3\pi} 2) = 2 (-1) = -2$ $y = 4 + cos(\frac {3\pi} 2) = 4 + 0 = 4$ - Since $sin(t)$ determines the $x$ position, and $cos(t)$ determines the $y$ position, the particle will move clockwise along the ellipse.
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