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 2 - First Order Differential Equations - 2.1 Linear Equations; Method of Integrating Factors - Problems - Page 39: 16

Answer

The solution of the initial value problem is $y=\dfrac {\sin{t}}{t^2}$.

Work Step by Step

By, comparing the differential equation with the linear form $y'+P(t)y=Q(t)$ We get, $P(t)=\dfrac{2}{t}$ Thus, the integrating factor $u(t)=e^{\int \frac{2}{t}\, dt}$ $\implies u(t)=e^{2\,ln(t)+c}=e^{2\,ln(t)}e^c$ Now multiply the equation by $u(t)$ on both sides. We get, $e^{2\,ln(t)}e^cy'+e^{2\,ln(t)}e^c\dfrac{2}{t}y=e^{2\,ln(t)}e^c\cdot\dfrac{\cos{t}}{t^2}$ Now integrate on both sides We get, $ e^{2\,ln(t)}y=\int e^{2\,ln(t)}\cdot\frac{\cos{t}}{t^2}\,dt$ Now simplify as follows; $ e^{ln(t^2)}y=\int e^{ln(t^2)}\cdot\frac{\cos{t}}{t^2}\,dt$ $\implies t^2y=\int t^2\cdot\frac{\cos{t}}{t^2}\,dt$ $\implies t^2y=\int \cos{t}\,dt$ $\implies t^2y= \sin{t}+c$ Substitute the initial condition $y(\pi)=0$ We get, $\pi^20= \sin{\pi}+c$ $\implies c=0$ Hence, the solution of the initial value problem is $y=\dfrac {\sin{t}}{t^2}$.
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