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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
>
>
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