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: 16

Answer

$${y}=\frac{3c_{1}e^{\frac{2+x}{2}}-c_{2}e^{\frac{-(x+2)}{2}}}{2}$$

Work Step by Step

$$4y''-y=0,\quad{y}(-2)=1,\quad{y'}(-2)=1$$Let $y=e^{\lambda{x}}$ so that $(\ln{y})'=\lambda$. $$4{\lambda}^2-1=0$$ $$\lambda_{1,2}=\pm\frac{1}{2}$$ The general solution is ${y}=c_{1}e^{\frac{x}{2}}+c_{2}e^{-\frac{x}{2}}$. Substituting in the constraints, we obtain $c_{1}e^{-1}+c_{2}e=1$ and $\frac{$c_{1}e^{-1}-c_{2}e}{2}=1\Rightarrow{c}_{1}e^{-1}=1-c_{2}e\Rightarrow\frac{1-2{c}_{2}e}{2}=1\Rightarrow{c}_{2}=-\frac{1}{2e}\Rightarrow{c}_{1}=\frac{3e}{2}$. $$\therefore{y}=\frac{3c_{1}e^{\frac{2+x}{2}}-c_{2}e^{\frac{-(x+2)}{2}}}{2}$$
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