Finish this problem? (Diff Eq)

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In summary, the given equation can be solved by separating variables, using partial fraction decomposition, and applying properties of e. The final solution is x(t)=\frac{C}{C-e^{-t}}.
  • #1
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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  • #2
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
 
  • #3
It was 95% complete, just to collect terms.
 
  • #4
I don't know why I didn't see that before... Maybe I was just too tired.. Thank you.
 

What is a differential equation?

A differential equation is a mathematical equation that describes the relationship between a function and its derivatives. It is used to model many real-world phenomena, such as the growth of populations, the flow of fluids, and the motion of objects.

What is the purpose of solving a differential equation?

The purpose of solving a differential equation is to find a function that satisfies the equation. This function can then be used to predict the behavior of the system being modeled.

What methods are used to solve differential equations?

There are several methods for solving differential equations, including separation of variables, substitution, and integrating factors. Advanced techniques such as Laplace transforms and numerical methods are also used for more complex equations.

What is the difference between ordinary and partial differential equations?

An ordinary differential equation (ODE) involves a single independent variable, while a partial differential equation (PDE) involves multiple independent variables. ODEs are used to model one-dimensional systems, while PDEs are used for multi-dimensional systems.

What are some real-world applications of differential equations?

Differential equations are used in many fields, including physics, engineering, biology, economics, and finance. They can be used to model the spread of diseases, the flow of electricity, the growth of populations, and many other phenomena.

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