Unique solution of 1st order autonomous, homogeneous DE

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Discussion Overview

The discussion revolves around the unique solution of first-order autonomous homogeneous differential equations, specifically the form \(\dot{x}(t) = ax(t)\). Participants explore the implications of this equation and the nature of its solutions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that the unique solution to the equation is given by \(x(t) = e^{at}x(t_0)\) and seeks clarification on this result.
  • Another participant questions the understanding of derivatives, specifically asking about the derivative of \(e^{at}\) and the expression \(e^{at}x(t_0)\).
  • A participant expresses confusion regarding the notation \(x(t) = x\) and clarifies that \(x(t)\) is indeed a function of \(t\).
  • Concerns are raised about calculating the integral of \(x(t)\) without knowing its specific form, with examples provided that illustrate potential variations of \(x(t)\).
  • One participant emphasizes that if \(\frac{dx}{dt} = ax\), the integration process involves only \(x\) as a variable, not \(t\).

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the understanding of the solution and the integration process. There is no consensus on how to approach the problem or the implications of the solution presented.

Contextual Notes

Participants highlight limitations in their understanding of the function \(x(t)\) and its derivatives, as well as the challenges in integrating without a specific form of \(x(t)\). The discussion reflects uncertainty about the relationship between the variables involved.

Pietair
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Hello,

1st order autonomous, homogeneous differential equation have the general form:
\dot{x}(t)=ax(t)

It can be shown that the unique solution is always:

x(t)=e^{at}x(t_{0})

I don't get this, could anyone help me?

Thanks!
 
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Have you tried at all? What is the derivative of e^{at}. Since x(t_0) is a constant, what is the derivative of e^{at}x(t_0)?
 
Thank you for your answer.

I can work it out when x(t) = x, but this is not the case, is it?
 
x(t) is supposed to be a function of t. What do you mean by x(t)=x?
 
How can I calculate the integral of x(t) when I don't know the corresponding function? x(t) can equal (t^2) or (t-3) and so on, right?
 
Will you please answer my questions? Do you know what the derivative of e^{at} is? Do you know what the derivative of e^{at}x(t_0) is?
 
Pietair said:
How can I calculate the integral of x(t) when I don't know the corresponding function? x(t) can equal (t^2) or (t-3) and so on, right?
You can't and you don't want to.

If \frac{dx}{dt}= ax then
\frac{dx}{x}= adt

Integrate both sides of
\int \frac{dx}{x}= \int a dt

Note that on the left you have NO "t". The only variable is x.
 

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