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 - 2.2 Separable Equations - Problems - Page 49: 29

Answer

($\frac{cy}{a}$)+ ($\frac{1}{a}$)(d-($\frac{cb}{a}$)ln(ay+b)=x+K

Work Step by Step

Question: $\frac{dy}{dx}$=$\frac{ay+b}{cy+d}$ 1. Separate the equation putting all variables with x on one side and y on the other by cross multiplying: dy(cy+d)=dx(ay+b) $\frac{cy+d}{ay+b}$dy=dx 2.Integrate both sides, left side with respect to y and the right side with respect to x. Since $\frac{cy+d}{ay+b}$ cannot simply be integrated, you have to first separate it into partial fractions. So in order to do that, according to the rules of partial fractions since the order of y on the denominator and numerator is the same we have to first proceed with long division as shown in the picture. According to the rules of long division theorem : 7 divided by 3 will give 2 and a remainder of 1 so: 3 x 2 +1 = 7 so using this we can now get the partial fractions: $\frac{ay+b}{ay+b}$($\frac{c}{a}$)+$\frac{(d-cb/a)}{ay+b}$=$\frac{cy+d}{ay+b}$ cancelling the two ay+b on the left side we get our partial fractions: ($\frac{c}{a}$)+$\frac{(d-cb/a)}{ay+b}$=$\frac{cy+d}{ay+b}$ 3. Now we can easily integrate it and get our final answer(Note that the integration of dx on the right side which is dx is just x because it is the integration of 1 and K is just a constant) ($\frac{cy}{a}$)+($\frac{1}{a}$)(d-$\frac{cb}{a}$)ln(ay+b)=x + K
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