Differential Equations and Linear Algebra (4th Edition)

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

Chapter 1 - First-Order Differential Equations - 1.2 Basic Ideas and Terminology - Problems - Page 22: 37

Answer

\[y=\frac{x^3}{3}\ln x-\frac{x^3}{9}+\frac{19}{9}\]

Work Step by Step

\[y'=x^2\ln x\] \[\frac{dy}{dx}=x^2\ln x\] Seperating the variables \[dy=x^2\ln x dx\] Integrating \begin{eqnarray*} y&=&\ln x\int x^2dx-\int \left(\frac{d}{dx}(\ln x)\int x^2dx\right)dx+c\\ &=&\frac{x^3}{3}\ln x-\int \frac{x^3}{3x}dx+c\\ &=&\frac{x^3}{3}\ln x-\frac{1}{3}\int x^2dx+c\\ &=&\frac{x^3}{3}\ln x-\frac{x^3}{9}+c \end{eqnarray*} Using initial condition $y(1)=2$ $2=\frac{1}{3}\ln 1-\frac{1}{9}+c \Rightarrow c=2+\frac{1}{9}=\frac{19}{9}$ Hence solution is $y=\frac{x^3}{3}\ln x-\frac{x^3}{9}+\frac{19}{9}$
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