Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 17 - Second-Order Differential Equations - 17.1 Exercises - Page 1172: 17

Answer

$y=-e^{4x}+3e^{2x}$

Work Step by Step

$y''-6y'+8y=0$ Use auxiliary equation $r^{2}-6r+8=0$ $(r-4)(r-2)=0$ $r_{1}=4$ $r_{2}=2$ Formula 8 $y=c_{1}e^{r_{1}x}+c_{2}e^{r_{2}x}$ $y=c_{1}e^{4x}+c_{2}e^{2x}$ Given: $y(0)=2$ $e^{0}=1$ $y(0)=2=c_{1}e^{4(0)}+c_{2}e^{2(0)}$ $c_{1}+c_{2}=2$ $y'(0)=2=4c_{1}e^{4(0)}+2c_{2}e^{2(0)}$ $4c_{1}+2c_{2}=2$ $c_{1}+c_{2}=2$ $4c_{1}+2c_{2}=2$ Use substitution to solve for $c_{1}$ and $c_{2}$ $c_{1}=2-c_{2}$ $4(2-c_{2})+2c_{2}=2$ $8-4c_{2}+2c_{2}=2$ $-2c_{2}=-6$ $c_{2}=3$ $c_{1}=2-c_{2}$ $c_{1}=3-2$ $c_{1}=-1$ $y=-e^{4x}+3e^{2x}$
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