How Can I Solve This Complex Differential Equation?

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Discussion Overview

The discussion revolves around solving a complex differential equation for y as a function of x. The equation involves several constants and participants are exploring methods to obtain an explicit solution.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant presents a differential equation and seeks methods for solving it explicitly for y in terms of x.
  • Another participant suggests that separation of variables could be an effective method for solving the equation.
  • A different participant expresses the need for y to be an explicit function of x, indicating that separation of variables would yield x as a function of y, which is not useful for their purpose.
  • One participant argues that while separation of variables may lead to x as a function of y, it is possible to find the inverse function to express y in terms of x, but notes potential issues with invertibility and expressibility in elementary functions.
  • There is a suggestion that separation of variables remains the appropriate approach despite the complications mentioned regarding invertibility and the form of the inverse function.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of separation of variables, with some supporting it as the only method while others highlight its limitations for obtaining y explicitly as a function of x. The discussion remains unresolved regarding the best approach to take.

Contextual Notes

Participants note potential issues with the invertibility of the function obtained from separation of variables and the possibility that the inverse may not be expressible in elementary functions, but these aspects are not fully explored or resolved.

JulieK
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I have the following differential equation which I want to solve for [itex]y[/itex] as a function of [itex]x[/itex]

[itex]\frac{dy}{dx}=\frac{C_{1}\left(C_{5}y+C_{6}\right)^{2}}{C_{2}\left(C_{3}y+C_{4}\right)-C_{7}\left(C_{5}y+C_{6}\right)^{6}}[/itex]

where [itex]C_{1},C_{2},C_{3},C_{4},C_{5},C_{6},C_{7}[/itex] are constants.
Can anyone suggest a method for solving this equation.
 
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separation of variables should do.
 
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I want y as an explicit function of x not the other way round.
The separation and integration will produce x as a function of y which is not very useful for my purpose.
 
You will get [itex]x[/itex] as a function of [itex]y[/itex], say [itex]f(y) = x[/itex]. Then you can try and find the inverse to get [itex]y[/itex] as a function of [itex]x[/itex], i.e. [itex]y = f^{-1}(x)[/itex]. There are a few things that can go wrong. If [itex]f[/itex] is not invertible then that tells you that there is no unique solution [itex]y(x)[/itex] to the differential equation. Otherwise, another thing that can go wrong is the inverse cannot be written down in terms of elementary functions.

So separation of variables is still the right (only?) approach. It won't change any of the facts above ([itex]f[/itex] invertible and inverse can be written down).
 

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