Solving a Differential Equation with a Substitution

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Discussion Overview

The discussion revolves around solving a differential equation through various substitution methods. Participants explore different approaches to simplify the equation and identify effective substitutions.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant presents the differential equation and expresses uncertainty about which substitution to use, having tried v = xy and v = y/x without success.
  • Another participant suggests using the substitution y = xv, noting it is applicable for homogeneous equations, although they express uncertainty about their expertise.
  • A later reply acknowledges the suggestion and admits to not checking it properly, indicating a realization of its validity.
  • Another participant proposes refactoring the left-hand side of the equation and suggests trying u = 2x + y, which they believe will simplify the problem and lead to a further substitution v = u^2.
  • The final reply confirms that this latter approach worked well and suggests it may have been the intended solution.

Areas of Agreement / Disagreement

Participants generally agree on the effectiveness of the substitution y = xv, while the discussion remains open regarding the best approach to take, with multiple suggestions presented.

Contextual Notes

Some assumptions about the nature of the differential equation and the applicability of certain substitutions remain unexamined, and the discussion does not resolve which substitution is definitively superior.

Who May Find This Useful

Students and individuals interested in differential equations, particularly those exploring substitution methods for solving such equations.

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I have the differential equation:

[tex]4(2x^2 + xy) \frac{dy}{dx} = 3y^2 + 4xy[/tex]

The only thing I could see working is a substitution, but I can't work out which one to use. I've tried letting v = xy, or v = y/x, but neither of those seem to produce anything useful. Can anyone give me a hint?
 
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i thought it was supposed to be y=xv... that's for the homogeneous ones i think. i am not expert though i am in the class right now myself.
 
You're right, y = vx does work... sorry, idiotic me didn't even check it properly. Thanks!
 
Refactor the left hand side to 4x(2x+y)dy/dx. This suggests trying u=2x+y. This will simplify nicely, and should in turn suggest trying v=u2.
 
Thanks, that worked out even better -- I think that may have been the intended solution.
 

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