Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 8 - Mathematical Modeling With Differential Equations - 8.4 First-Order Differential Equations And Applications - Exercises Set 8.4 - Page 592: 7

Answer

$$y=\frac{1}{2}x+\frac{3}{2x} $$

Work Step by Step

Given $$x \frac{dy}{dx} + y =x,\ \ \ \ \ y(1)=2$$ Rewriting the equation $$ \frac{dy}{dx} +\frac{1}{x} y=1$$ Since \begin{align*} \mu(x)&=e^{\int \frac{1}{x} dx}\\ &=e^{\ln x } \\ &=x \end{align*} Then \begin{align*} y\mu(x)&=\int \mu(x) q(x)dx\\ x y&=\int x dx\\ &=\frac{1}{2}x^2+c \end{align*} since $y(1)=2,$ then $c= \frac{3}{2}$ Hence $$y=\frac{1}{2}x+\frac{3}{2x} $$
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