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 - 8.1 Modeling With Differential Equations - Exercises Set 8.1 - Page 567: 25

Answer

$$y = \frac{2}{{{x^2}}},{\text{ where }}x > 0$$

Work Step by Step

$$\eqalign{ & {x^2}y' + 2xy = 0,{\text{ }}y\left( 1 \right) = 2 \cr & {\text{The left - hand side can be interpreted as the derivative of the}} \cr & {\text{product }}{x^2}y.{\text{ }}\frac{d}{{dx}}\left[ {{x^2}y} \right] = {x^2}y' + 2xy,{\text{ then,}} \cr & {x^2}y' + 2xy = 0 \cr & \frac{d}{{dx}}\left[ {{x^2}y} \right] = 0 \cr & {\text{Integrate both sides with respect to }}x \cr & {x^2}y = C \cr & {\text{Solve for }}y \cr & y = \frac{C}{{{x^2}}} \cr & {\text{Use the initial condition }}y\left( 1 \right) = 2 \cr & 2 = \frac{C}{{{{\left( 1 \right)}^2}}} \Rightarrow C = 2 \cr & {\text{,then}} \cr & y = \frac{2}{{{x^2}}},{\text{ where }}x > 0 \cr} $$
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