Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 9: First-Order Differential Equations - Section 9.2 - First-Order Linear Equations - Exercises 9.2 - Page 538: 31

Answer

$y=(1+\dfrac{c}{x^3})^{1/3}$

Work Step by Step

On comparing the equation $xy'+y=y^{-2}$ with Bernoulli with $n=-2$ Consider $p=y^{1-(-2)}=y^{3}$ Then $\dfrac{dy}{dx}=(\dfrac{p^{-2/3}}{3})\dfrac{dp}{dx}$ $\implies \dfrac{dp}{dx}+\dfrac{3p}{x}=\dfrac{3}{x}$ The integrating factor is: $I=e^{\int (\frac{3}{x})dx}=x^{3}$ $x^{3}[\dfrac{dp}{dx}+\dfrac{3p}{x}]=x^{3}(\dfrac{3}{x})$ This gives: $\int [x^3u]'=\int 3x^2 dx$ $\implies p=1+cx^{-3}$ Thus, $y^3=1+cx^{-3} \implies y=(1+\dfrac{c}{x^3})^{(1/3)}$
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