2nd order ODE with Sin function.

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Discussion Overview

The discussion revolves around solving a second-order differential equation of the form d²X/dt² + dX/dt + sin(X) = 0. Participants explore the nature of the equation, its solvability, and potential methods for finding solutions, including the possibility of a typo in the equation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses familiarity with solving second-order differential equations but questions how to approach this specific equation.
  • Another participant notes that the equation is not linear and questions its solvability, suggesting that Mathematica cannot solve it.
  • A participant wonders if the original equation might have been intended to use sin(t) instead of sin(X), proposing that this could lead to a solvable form.
  • Hints are provided for solving the equation if it is indeed sin(t), including a method to find the complementary and particular solutions.
  • One participant requests further clarification on solving the equation if it is sin(X), indicating curiosity about the implications of the original form.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the solvability of the original equation. There is uncertainty regarding whether the equation should use sin(X) or sin(t), and multiple viewpoints are presented without resolution.

Contextual Notes

The discussion highlights the potential for a typo in the equation, which may affect the approach to solving it. The participants express varying degrees of confidence in the methods discussed, and there are unresolved assumptions about the equation's form.

Who May Find This Useful

Students and enthusiasts of differential equations, particularly those interested in nonlinear dynamics and methods of solving second-order ODEs.

rizvi71
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Hey guys!
I'm trying to solve a 2nd order differential equation. I am quite familiar with the method of solving these equations like treat them like characteristic equation ODE.
but there's a question which I really want to solve.
question is d^2 X/dt^2 +dX/dt +sinX=0.
How should I solve this??
 
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rizvi71 said:
Hey guys!
I'm trying to solve a 2nd order differential equation. I am quite familiar with the method of solving these equations like treat them like characteristic equation ODE.
but there's a question which I really want to solve.
question is d^2 X/dt^2 +dX/dt +sinX=0.
How should I solve this??

That is not a linear ode and mathematica can't solve it... Is it solvable?
 
Hmmmm... my teacher gave me an assignment to solve this. So are you implying that its unsolvable??
 
rizvi71 said:
Hmmmm... my teacher gave me an assignment to solve this. So are you implying that its unsolvable??

Maybe he meant to write sint instead of sinx. If that's the case, then the solution is easy to find. Otherwise, unless you use some kind of "trick" I don't see how you can solve it
 
could you please give me some kind of a hint??
If it is "sint" how can i solve it??
 
rizvi71 said:
could you please give me some kind of a hint??
If it is "sint" how can i solve it??

Sure I can(if it is sint)

\begin{array}\\x''+x'+sint=0\\
x(t)=x_0(t)+x_p(t)\\
x_0''+x_0'=0\\
r^2+r=0\Leftrightarrow r(r+1)=0\Leftrightarrow r_1=0, r_2=-1\\
x_0(t)=c_1e^{0t}+c_2e^{-t}=c_1+c_2e^{-t}\end{array}

Let [tex]x_p=Asint+Bcost[/tex]
Then
\begin{array}\\x''_p+x'_p+sint=0\Leftrightarrow (Asint+Bcost)''+(Asint+Bcost)'+sint=0\\-Asint-Bcost+Acost-Bsint+sint=0\Leftrightarrow sint(-A-B+1)+cost(-B+A)=0
\\\begin{Bmatrix}
-A& -B& =-1\\
-B& +A& =0
\end{Bmatrix}\Leftrightarrow \begin{Bmatrix}
B& +B& =1\\
& A& =B
\end{Bmatrix}\Rightarrow 2B=1\Leftrightarrow B=\frac{1}{2}=A\\
x_p=\frac{1}{2}(sint+cost)
\end{array}

Therefore, [tex]x(t)=c_1+c_2e^{-t}+\frac{1}{2}(sint+cost)[/tex]
 
thanx a lot buddy !
Really appreciate it !
 
rizvi71 said:
thanx a lot buddy !
Really appreciate it !

No problem. Just ask your teacher and tell me whether it is sint or sinx.
 
Yeah sure will.
In the mean time can you please work something out if it is sinx. I'm really curious about this question.
 

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