Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 10 - The Laplace Transform and Some Elementary Applications - 10.7 The Second Shifting Theorem - Problems - Page 705: 28

Answer

See below

Work Step by Step

We are given that $y'-2y=u_2(t)e^{t-2}$ and $y(0)=2$ We take the Laplace transform of both sides of the differential equation to obtain: $[sY(s)-y(0)]-2Y(s)=\frac{e^{-2s}}{s-1}$ Substituting in the given initial values and rearranging terms yields $Y(s)(s^2-2)-2=\frac{e^{-2s}}{s-1}\\ Y(s)(s^2-2)=\frac{e^{-2s}}{s-1}+2$ Thus, we have solved for the Laplace transform of $y(t)$. To find y itself, we must take the inverse Laplace transform. We first decompose the right-hand side into partial fractions to obtain: $Y(s)=\frac{e^{-2s}}{(s-1)(s-2)}+\frac{2}{s-2}\\ =e^{-2s}(\frac{1}{s-2}-\frac{1}{s-1})+\frac{2}{s-2}$ Now,$f(t)= L^{-1}[e^{-2s}(\frac{1}{s-2}-\frac{1}{s-1})+\frac{2}{s-2}]\\ =e^{2(t-2)})u_2(t)+e^{t-2}u_3(t)+2e^{2t}$
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