University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 16 - Section 16.2 - First-Order Linear Equations - Exercises - Page 16-15: 32

Answer

$y=(\dfrac{2}{5x}+cx^{4})^{-1/2}$

Work Step by Step

Here, we have $x^2y'+2xy=y^{3}$ Compare the above equation with the Bernoulli equation with $n=3$ Plug $u=y^{1-(3)}=y^{-2}$ or, $y=u^{-1/2}$ Then $\dfrac{dy}{dx}=(\dfrac{-1}{2})u^{-3/2}\dfrac{du}{dx}$ or, $\dfrac{du}{dx}-\dfrac{4}{x}u=-\dfrac{2}{x^2}$ The integrating factor is: $e^{\int (\frac{-4}{x})dx}=x^{-4}$ In order to determine the general solution, multiply equation (1) with the integrating factor and integrate both sides. $\int [ux^{-4}]'=(-2) \int x^{-6} dx$ or, $u=\dfrac{2}{5x}+cx^{4} \implies y^{-2}=\dfrac{2}{5x}+cx^{4}$ Thus, $y=(\dfrac{2}{5x}+cx^{4})^{-1/2}$
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