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 - 1.11 Some Higher-Order Differential Equations - Problems - Page 105: 8

Answer

$y=\frac{x^6}{3}+C_1x^3+C_2$

Work Step by Step

We are given: $y''-2x^{-1}y'=6x^4$ Suppose that $u=\frac{dy}{dx}$ Now, $\frac{du}{dx}=\frac{d^2y}{dx^2}$ Subsitute to the equation: $\frac{du}{dx}-2x^{-1}u=6x^4$ Integrating factor: $I(x)=e^{\int =2x^{-1}dx}=e^{-2\ln x}=x^{-2}$ The equation becomes: $\frac{d}{dx}(ux^{-2})=6x^2$ Integrating both sides: $ux^{-2}=2x^3+C$ $ u=2x^5+Cx^2$ $\frac{dy}{dx}=2x^5+Cx^2$ $dy=(2x^5+Cx^2)dx$ Integrating the last equation, $y=\frac{x^6}{3}+C_1x^3+C_2$ The final solution is: $y=\frac{x^6}{3}+C_1x^3+C_2$
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