Elementary Differential Equations and Boundary Value Problems 9th Edition

Published by Wiley
ISBN 10: 0-47038-334-8
ISBN 13: 978-0-47038-334-6

Chapter 1 - Introduction - 1.1 Some Basic Mathematical Models; Direction Fields - Problems - Page 8: 9

Answer

$\frac{dy}{dt}=y-2$, a=-2, b=1

Work Step by Step

For equations of the form $\frac{dy}{dt}=a+by$, all equilibrium solutions (called $y_{eq}$) can be found by solving the right side of the equation for $\frac{dy}{dt}=0$. The solution of this ($0=a+by$) is $y=-\frac{a}{b}$. If $b\lt0$, all values of $y$ such that $y{\ne}y_{eq}$ will be convergent. If $b\gt0$, all values of $y$ such that $y{\ne}y_{eq}$ will be divergent. Our problem specifies that $y_{eq}=2$, therefore $-\frac{a}{b}=2$. Any values of $a$ and $b$ that satisfy this, and where $b\gt0$ will be solutions.
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