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 - 2.9 First Order Difference Equations - Problems - Page 132: 4

Answer

$y=-3+Ce^{x-x^2}$

Work Step by Step

This equation can be rewritten as the following: $$\frac{dy}{dx}+(2x-1)y =3-6x$$ Multiplying both sides by the integrating factor of $e^{x^2-x}$ gives $$e^{x^2-x}y' + (2x-1)e^{x^2-x}y=(3-6x)e^{x^2-x}$$ Therefore, by product rule, $$\frac{d}{dx}(e^{x^2-x}y)=3(1-2x)e^{x^2-x}$$ The integral of the left side of the equation becomes $e^{x^2-x}$. The integral of the right side requires a u-substitution of $u=x^2-x$. Therefore, $du=(2x-1)dx$ and $-3du = 3(1-2x) dx$ Thus, the integral of the right side becomes $$-3 \int e^udu = -3e^u+C=-3e^{x^2-x}+C$$ Therefore, $e^{x^2-x}y = -3e^{x^2-x}+C$ meaning that $$y=e^{x-x^2}(-3e^{x^2-x}+C)=-3+Ce^{x-x^2}$$
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