       Re: Differential equation

• To: mathgroup at smc.vnet.net
• Subject: [mg69493] Re: Differential equation
• From: dimmechan at yahoo.com
• Date: Thu, 14 Sep 2006 06:55:32 -0400 (EDT)
• References: <ee8gca\$imk\$1@smc.vnet.net>

```***You have one differentai equation for two dependent variables.
***You need one more equation.

diff=x[t]-A*D[y[t],t]==0;

DSolve[diff,{x[t],y[t]},t]
DSolve::underdet: The system has more dependent variables than
equations, so is underdetermined. Moreâ?¦
DSolve[x[t] - A*Derivative[y][t] == 0, {x[t], y[t]}, t]

***But e.g.

diff1=x[t]-A*D[y[t],t]==0;
diff2=D[x[t],t]+y[t]==2;

DSolve[{diff1,diff2},{x[t],y[t]},t]
{{y[t] -> C*Cos[t/Sqrt[A]] + 2*Cos[t/Sqrt[A]]^2 +
(C*Sin[t/Sqrt[A]])/Sqrt[A] + 2*Sin[t/Sqrt[A]]^2, x[t] ->
C*Cos[t/Sqrt[A]] - Sqrt[A]*C*Sin[t/Sqrt[A]]}}

***Cheers
Dimitris
Î?/Î? Mike Î­Î³Ï?Î±Ï?Îµ:
> Dear all,
>
> I do not know how to solve this differential equation :
>
> x(t)-A*dy/dt=0
>
> Where,
> A - constant
> x - variable as a function of time (t)
> y - variable as a function of time (t)
> t - time
>
>
> Thanks Mike77

```

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