Differential Equation-Separable Equations

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Homework Help Overview

The discussion revolves around solving a differential equation involving separable variables, specifically the equation xcosx=(2y + e^(3y)) y' with the initial condition y(0)=0. Participants are exploring the implications of substituting values into the equation based on the initial condition.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the correct substitution of initial conditions into the equation, questioning whether to substitute values for x or y. There is also mention of a potential sign error in the derived solution.

Discussion Status

Some guidance has been provided regarding the substitution of initial conditions, with participants clarifying the relationship between the variables in different contexts. There is an ongoing exploration of how to handle different initial conditions in related problems.

Contextual Notes

Participants are navigating the nuances of variable dependence in differential equations, particularly when transitioning between different problems with varying initial conditions.

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Homework Statement


Find the solution of the diff eq that satisfies the given initial coordinate


Homework Equations


xcosx=(2y + e^(3y)) y' , y(0)=0


The Attempt at a Solution



So I have the family of solutions:
xsinx-cosx=y^2 + e^(3y)/3 + c

and I know to put 0 in for the x's, but the solution is wrong, and it appears like I need to put 0 into the y's (yes I did say y's) but not sure why.
 
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neshepard said:

Homework Statement


Find the solution of the diff eq that satisfies the given initial coordinate


Homework Equations


xcosx=(2y + e^(3y)) y' , y(0)=0


The Attempt at a Solution



So I have the family of solutions:
xsinx-cosx=y^2 + e^(3y)/3 + c

and I know to put 0 in for the x's, but the solution is wrong, and it appears like I need to put 0 into the y's (yes I did say y's) but not sure why.
Yes, substitute 0 for x and 0 for y. That's what y(0) = 0 means.

You have a sign error in your solution. It should be xsinx + cosx = y^2 + e^(3y) + C.
 
Thanks for the reply. And just to clarify, I have another problem where the initial condition is u(0)=-5 so I put in -5 for my x's and 0 for my y's?
 
neshepard said:
Thanks for the reply. And just to clarify, I have another problem where the initial condition is u(0)=-5 so I put in -5 for my x's and 0 for my y's?

If x is the dependent variable, that is, you have u(x), then you need to set x=0 and u=-5. You don't have x and y anymore, one of them has been replaced by a new function u in this other problem.
 
Nice...thanks.
 

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