Re: Plot using DSolve HELP

*To*: mathgroup at smc.vnet.net*Subject*: [mg104418] Re: [mg104388] Plot using DSolve HELP*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sat, 31 Oct 2009 01:50:51 -0500 (EST)*Reply-to*: hanlonr at cox.net

Your eq is not an equation, it is an expression. I don't know how you got a result from DSolve eq = i*v[t]/r + c v'[t] == -2/5; Use exact numbers with DSolve sol[t_] = v[t] /. DSolve[{eq /. {c -> 3, i -> 0, r -> 5/2}, v[0] == -70}, v[t], t][[1]] -(2/15) (t+525) Plot[sol[t], {t, -20, 140}] Bob Hanlon ---- Becky <noslowski at comcast.net> wrote: ============= I have a problem with what I am showing below. Step one is my equation. eq = i * v[t]/r +c v'[t] Step two I want to solve it, using DSolve, and put my values in as shown. Please note, that "i= 0", and my IC is v[0]== -70. sol=v[t]/.DSolve[{eq/.{c->3, i->0, r->2.5} ,v[0]==-70}, v[t], t] {-70 *-0.133333 t} The results are shown above. Thus next step is to plot it. p1=Plot[sol,{t,-20,140}] My problem is that I get a line from -70 on the vertical axis going in a curve up to the horizontal axis out to 140. The vertical axis is "v" and the horizontal is "t". What am I doing wrong? Thanks Jake