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[1][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[1]*Cos[t/Sqrt[A]] + 2*Cos[t/Sqrt[A]]^2 + (C[2]*Sin[t/Sqrt[A]])/Sqrt[A] + 2*Sin[t/Sqrt[A]]^2, x[t] -> C[2]*Cos[t/Sqrt[A]] - Sqrt[A]*C[1]*Sin[t/Sqrt[A]]}} ***Cheers Dimitris Î?/Î? Mike ÎÎ³Ï?Î±Ï?Îµ: > Dear all, > > I would kindly ask for an assistance please. > 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