Finish this problem? (Diff Eq)

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Homework Help Overview

The discussion revolves around solving a differential equation of the form \(\frac{dx}{dt}=x-x^{2}\). Participants are examining the steps taken to separate variables and integrate, as well as the manipulation of the resulting expression.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the process of separating variables and integrating, with one noting a potential issue in reaching the final form of the solution. There is mention of partial fraction decomposition and the use of logarithmic properties.

Discussion Status

Some participants have provided guidance on isolating \(x\) to express the solution in the required form. There is acknowledgment of a nearly complete solution, with suggestions to collect terms and factor appropriately. However, there is no explicit consensus on the correctness of the final answer.

Contextual Notes

Participants are working under the constraints of homework expectations, which include presenting the solution in a specific format. There is also a mention of potential fatigue affecting the original poster's clarity in the problem-solving process.

iRaid
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Homework Statement


[tex]\frac{dx}{dt}=x-x^{2}[/tex]

Homework Equations


The Attempt at a Solution


I think the only thing I have wrong so far is how to finish it because I can't find anything wrong with my work, but I don't know how the book gets their final answer.
Separate variables...
[tex]\int \frac{dx}{x(1-x)}=\int dt[/tex]
Partial fraction decomposition..
[tex]\int (\frac{1}{x}-\frac{1}{x-1})dx=t+C\\ln|x|-ln|x-1|=t+C\\ln|\frac{x}{x-1}|=t+C[/tex]
Using properties of e...
[tex]\frac{x}{x-1}=e^{t}e^{C}[/tex]
D=e^C (professor wants us to write it like this) and multiply by x-1 on both sides..
[tex]x=De^{t}(x-1)[/tex]

That's not the solution though and I'm not sure why.
Final answer: [tex]x(t)=\frac{C}{C-e^{t}}[/tex]
 
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iRaid said:
[tex]x=De^{t}(x-1)[/tex]

That's not the solution though and I'm not sure why.
Final answer: [tex]x(t)=\frac{C}{C-e^{t}}[/tex]

You have to isolate x, writing the solution in the form x(t)=f(t). Expand your equation, collect the terms with x at one side, factor it ...

The final solution you quoted is not correct. There must be a minus in front of t in the exponent.

ehild
 
It was 95% complete, just to collect terms.
 
I don't know why I didn't see that before... Maybe I was just too tired.. Thank you.
 

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