Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 6 - Differential Equations - 6.1 Exercises - Page 403: 38

Answer

$\text{The general solution satisfies the differential equation.}$ $\text{The particular solution is $y = -\ln 2 + \ln x$.}$

Work Step by Step

$\text{Let us find the second derivative of the general solution:}$ \begin{align} & y = C_1 + C_2 \ln {x} \\ & y' = \frac{C_2}{x} \\ & y'' = -\frac{C_2}{x^2} \end{align} $\text{Then, substitute $y''$ and $y'$ into the differential equation}$ \begin{align} & xy''+y'=0 \\ -\frac{C_2}{x^2} &\times x + \frac{C_2}{x} = 0 \\ & \ \ 0 = 0 \end{align} $\text{Thus, the general solution satisfies the differential equation.}$ $\text{Now, we have to find the particular solution:}$ \begin{align} & y = 0 \ \ when \ \ x =2 \\ & 0 = C_1 + C_2\ln 2 \\ & y' = \frac{1}{2} \ \ when \ \ x =2 \\ & \frac{1}{2} = \frac{C_2}{2} \Rrightarrow C_2 = 1 \Rrightarrow C_1 = -\ln 2 \end{align} $\text{Thus, the particular solution is}$ \begin{align} y = -\ln 2 + \ln x \end{align}
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