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 3 - Second Order Linear Equations - 3.1 Homogenous Equations with Constant Coefficients - Problems - Page 144: 20

Answer

${y}=3e^{\frac{x}{2}}-e^{x},\quad{y}\rightarrow0\quad{as}\quad{x}\rightarrow-\infty$

Work Step by Step

$$2y''-3y'+y=0,\quad{y}(0)=2,\quad{y'}(0)=\frac{1}{2}$$ Let $y=e^{\lambda{x}}$ so that $(\ln{y})'=\lambda$. $$2{\lambda}^2-3{\lambda}+1=0$$ $$(2\lambda-1)(\lambda-1)=0$$ $$\lambda_{1,2}=\frac{1}{2},1$$ The general solution is ${y}=c_{1}e^{\frac{x}{2}}+c_{2}e^{x}$. Substituting in the constraints, we obtain $c_{1}+c_{2}=2$ and $\frac{c_{1}}{2}+c_{2}=\frac{1}{2}\Rightarrow\frac{c_{1}}{2}=\frac{3}{2}\Rightarrow{c}_{1}=3\Rightarrow{c}_{2}=-1$ $$\therefore{y}=3e^{\frac{x}{2}}-e^{x}$$ $\lim_{x\to\infty}y=+\infty$. The solution tends to zero when $x\rightarrow-\infty$.
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