C1 and C2 in a differential equation....

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Discussion Overview

The discussion revolves around the interpretation and notation of differential equations, specifically focusing on the equation d²x/dt = 0.01 - 0.01dx/dt and the constants c1 and c2 in its solution. Participants explore whether c1 and c2 are constants or functions, and the implications of using different notations for derivatives.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that c1 and c2 are constants that cannot be determined without initial conditions.
  • Others argue that the notation d²x/dt is incorrect and should be d²x/dt², leading to confusion regarding the interpretation of the equation.
  • One participant suggests that the same solution for both d²x/dt and d²x/dt² implies different values for c1 and c2, although this is contested.
  • There is a disagreement on the meaning of d²/dt, with some claiming it refers to ddx/dt, while others maintain it is meaningless in this context.
  • Participants discuss the merits of using modified Newton notation as a clearer alternative for expressing the equations.

Areas of Agreement / Disagreement

Participants do not reach consensus on the correct notation for the derivatives or the nature of c1 and c2. Multiple competing views remain regarding the interpretation of the differential equation and the implications of the notation used.

Contextual Notes

There are unresolved issues regarding the assumptions behind the notation and the definitions of the derivatives being discussed. The discussion reflects varying interpretations of mathematical notation and its implications for the solution of the differential equation.

luckis11
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d^2x/dt=0.01-0.01dx/dt
=>x(t)=-100c1(e^-0.01t)+c2+t
How do we find c1 and c2. Are they numbers or functions?
d^2x/dt^2 instead of d^2x/dt gives the same solution, which means different c1 and c2
 
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luckis11 said:
d^2x/dt=0.01-0.01dx/dt
=>x(t)=-100c1(e^-0.01t)+c2+t
How do we find c1 and c2. Are they numbers or functions?
d^2x/dt^2 instead of d^2x/dt gives the same solution, which means different c1 and c2
c1 and c2 are constants (numbers). You can't determine them without having initial conditions.

Some of your notation is screwy. d^2x/dt doesn't mean anything. It should be d^2x/dt^2, or better yet ##\frac{d^2x}{dt^2}##, which you could write more simply as x''(t).
 
d^2/dt means ddx/dt and the solution was from wolframalfa, thus you disagree with them. I don't have time to reassure that the same solution for d^2x/dt=0.01-0.01dx/dt and for d^2x/dt^2=0.01-0.01dx/dt simply means different c1 and c2.

From some of my calcultions it seems that in this case c1 c2 are numbers (in other cases I guess they are not), so ignore the initial question.
 
luckis11 said:
d^2/dt means ddx/dt and the solution was from wolframalfa, thus you disagree with them.

Woolfram alpha interprets the incorrect and meaningless "d^2x/dt" as the correct "d^2x/dt^2".
 
luckis11 said:
d^2/dt means ddx/dt
No it doesn't. As pasmith said, d^2/dt is incorrect and meaningless. Also, ddx/dt is equally incorrect and meaningless.

The notation ##\frac{d^2x}{dt^2}## is shorthand for ##\frac d {dt} ( \frac{dx} {dt})##.
 
My mistake d^2/dt meant d^2x/dt at the second post. You should leave more time to edit our posts.
d^2x MEANS ddx. That is, the difference between the last and the previous dx.
dddx=d^3x
When speed is increasing: ddx/dt=d(dx/dt)=du if all the dt are equal, whereas if all the dx are equal ddx=0
 
luckis11 said:
My mistake d^2/dt meant d^2x/dt at the second post.

It still does not make sense, whether you like it or not.
 
From your 2nd post (post #3):
luckis11 said:
I don't have time to reassure that the same solution for d^2x/dt=0.01-0.01dx/dt and for d^2x/dt^2=0.01-0.01dx/dt simply means different c1 and c2.
Above, your first equation is incorrect, because of the d^2x/dt term. This has been stated several times. The expression d^2x/dt could be correct, assuming you're talking about the differential of dx/dt, instead of the derivative of dx/dt, but from the context of these equations, you're dealing strictly with the first and second derivatives.
Personally, for equations such as this, modified Newton notation is simpler to write, either as x'' = .01 - .01x', or more explicitly as x''(t) = .01 - .01x'(t), showing t as the independent variable.
From post #6:
luckis11 said:
My mistake d^2/dt meant d^2x/dt at the second post.
Still incorrect. If you mean ##\frac d {dt}(\frac {dx}{dt})##, that is ##\frac{d^2x}{dt^2}##.
 

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