Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 6 - Differential Equations - 6.4 Exercises - Page 430: 61

Answer

$$y = \frac{1}{{Cx - {x^2}}}$$

Work Step by Step

$$\eqalign{ & y' + \left( {\frac{1}{x}} \right)y = x{y^2} \cr & {\text{The differential equation is written in the form}} \cr & y' + P\left( x \right)y = Q\left( x \right){y^n} \cr & y' + \left( {\frac{1}{x}} \right)y = x{y^2} \to P\left( x \right) = \frac{1}{x},{\text{ }}Q\left( x \right) = x,{\text{ }}n = 2 \cr & {\text{From the book we have that the general solution of a Bernoulli }} \cr & {\text{equation is:}} \cr & {y^{1 - n}}{e^{\int {\left( {1 - n} \right)P\left( x \right)dx} }} = \int {\left( {1 - n} \right)Q\left( x \right){e^{\int {\left( {1 - n} \right)P\left( x \right)dx} }}dx} + C{\text{ }}\left( {\bf{1}} \right) \cr & {\text{Find }}{e^{\int {\left( {1 - n} \right)P\left( x \right)dx} }} \cr & {e^{\int {\left( {1 - n} \right)P\left( x \right)dx} }} = {e^{\int {\left( {1 - 2} \right)\left( {\frac{1}{x}} \right)dx} }} = {e^{ - \int {\frac{1}{x}} dx}} = {e^{ - \ln \left| x \right|}} = \frac{1}{x} \cr & {\text{Substituting }}{e^{\int {\left( {1 - n} \right)P\left( x \right)dx} }},{\text{ }}n,{\text{ and }}Q\left( x \right){\text{ into }}\left( {\bf{1}} \right) \cr & {y^{1 - 2}}\left( {\frac{1}{x}} \right) = \int {\left( {1 - 2} \right)\left( x \right)\left( {\frac{1}{x}} \right)dx} + C{\text{ }} \cr & {y^{ - 1}}\left( {\frac{1}{x}} \right) = - \int {dx} + C{\text{ }} \cr & {\text{Integrating}} \cr & {y^{ - 1}}\left( {\frac{1}{x}} \right) = - x + C{\text{ }} \cr & {y^{ - 1}} = - {x^2} + Cx{\text{ }} \cr & {\text{Solve for }}y \cr & \frac{1}{y} = - {x^2} + Cx{\text{ }} \cr & y = \frac{1}{{Cx - {x^2}}} \cr} $$
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