Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 9 - Section 9.5 - Linear Equations - 9.5 Exercises - Page 625: 11

Answer

$y = x^2~ln~x+C~x^2,~~~~$ $x \gt 0$

Work Step by Step

A first-order linear differential equation is one that can be put into the form: $\frac{dy}{dx} + P(x)~y = Q(x)$ We can consider the given equation: $xy' - 2y = x^2$ $y' +(-\frac{2}{x})~y = x$ Let $P(x) = -\frac{2}{x}$ Let $Q(x) = x$ We can find the integrating factor: $I(x) = e^{\int -\frac{2}{x} ~dx} = e^{-2~ln(x)} = e^{ln(x^{-2})} = \frac{1}{x^2}$ We can multiply by the integrating factor: $\frac{1}{x^2}~y'-\frac{2}{x^3}~y = \frac{1}{x}$ $\frac{d}{dx}(\frac{1}{x^2}~y) = \frac{1}{x}$ We can integrate both sides of the equation: $\frac{1}{x^2}~y = \int \frac{1}{x}~dx$ $\frac{1}{x^2}~y = ln~x+C$ $y = x^2~ln~x+C~x^2,~~~~$ $x \gt 0$
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