Solving First Order Linear Differential Equation

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SUMMARY

The discussion focuses on solving the first-order linear differential equation given by (E): (x+1)²(xy' - y) = -(2x + 1). The equation is rearranged to the standard form y' - (y/x) = -(2x + 1)/(x(x + 1)²), and an integrating factor of 1/x is chosen. The general solution derived is y = 1/(x + 1) + kx, where k ∈ ℝ. The user seeks clarification on the validity of this solution across various intervals, particularly for I = (-1, +∞) and I = ℝ, due to potential issues at points 0 and -1.

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  • Understanding of first-order linear differential equations
  • Knowledge of integrating factors in differential equations
  • Familiarity with partial fraction decomposition
  • Basic calculus skills, particularly integration techniques
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  • Explore the concept of general solutions and particular solutions in differential equations
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Students and educators in mathematics, particularly those focusing on differential equations, as well as anyone looking to deepen their understanding of first-order linear differential equations and their solutions across specified intervals.

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Homework Statement



Given (E): [itex](x+1)^{2}(xy'-y) = -(2x+1)[/itex]

Determine the set of applications from the interval [itex]I[/itex] to [itex]ℝ[/itex] which are solutions of (E) for:

a) [itex]I = (0,+∞)[/itex]
b) [itex]I = (-1,0)[/itex]
c) [itex]I = (-∞,-1)[/itex]
d) [itex]I = (-1,+∞)[/itex]
e) [itex]I = ℝ[/itex]


The attempt at a solution

I have rearranged (E) into the form:

[itex]y'-\frac{y}{x}[/itex] = [itex]\frac{-(2x+1)}{x(x+1)^{2}}[/itex]

and chosen integrating factor:

[itex]exp(∫\frac{-1}{x}dx) = \frac{1}{x}[/itex]

now multiplying by the integrating factor and integrating gives:

[itex]∫\frac{y'}{x}-\frac{y}{x^{2}}dx = ∫\frac{-(2x+1)}{x^{2}(x+1)^{2}}dx[/itex]

partial fractions now give:

[itex]∫\frac{y'}{x}-\frac{y}{x^{2}}dx = ∫\frac{-1}{x^{2}}+\frac{1}{(x+1)^{2}}dx[/itex]

After integrating and a tiny bit of algebra I get a general solution, for [itex]k\inℝ[/itex] as:

[itex]y=\frac{1}{x+1}+kx[/itex]

Now I think I am right in saying that this solution works fine for the intervals in a), b) and c)?

However for [itex]I = (-1,+∞)[/itex] there is (or potentially is) a problem with the point [itex]0[/itex] and for [itex]I = ℝ[/itex] there are (or potentially are) problems with the points [itex]0[/itex] and [itex]-1[/itex]?

Now I'm not sure how to proceed. Am I thinking along the right lines?

Any help/pointers would be very much appreciated, Thanks!
 
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Can the general solution already posted simply extend to [itex]I = (-1,+∞)[/itex] ??
If so how can this be shown in detail?

Also I don't yet understand what happens when we are considering [itex]ℝ[/itex]

Thanks for any help!
 

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