Re: Plot using DSolve HELP

*To*: mathgroup at smc.vnet.net*Subject*: [mg104419] Re: Plot using DSolve HELP*From*: "Kevin J. McCann" <Kevin.McCann at umbc.edu>*Date*: Sat, 31 Oct 2009 01:51:03 -0500 (EST)*References*: <hce3uu$r15$1@smc.vnet.net>

Your differential equation, eq, is not set equal to anything. perhaps you meant eq = i * v[t]/r +c v'[t] == 0 With i = 0, then v'=0 and the answer is just a constant -70. Kevin Becky 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 > >