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 6 - The Laplace Transform - 6.2 Solutions of Initial Value Problems - Problems - Page 320: 7

Answer

$2e^{t} \cos t+3e^{t} \sin t$

Work Step by Step

Since, $\mathcal{L}(e^{at} \cos bt)=\dfrac{s-a}{(s-a)^2+b^2}$ and $\mathcal{L}(e^{at} \sin bt)=\dfrac{b}{(s-a)^2+b^2}$ Here, we have $F(S)=\dfrac{2s+1}{s^2-2s+2}$ or, $= \dfrac{2s-2+3}{s^2-2s+2}$ or, $=2 [\dfrac{s-1}{(s-1)^2+(1)^2}] +3 [\dfrac{1}{(s-1)^2+(1)^2}] $ or, $=2\mathcal{L}(e^{t} \cos t)+3\mathcal{L}(e^{t} \sin t)$ or, $=\mathcal{L}(2e^{t} \cos t+3e^{t} \sin t)$ Therefore, the required inverse Laplace transform is: $\mathcal{L}^{-1}[\mathcal{L}(2e^{t} \cos t+3e^{t} \sin t)]=2e^{t} \cos t+3e^{t} \sin t$
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