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Re: Result to DEQ with WA versus Step-by-Step Yields

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  • Subject: [mg132311] Re: Result to DEQ with WA versus Step-by-Step Yields
  • From: amzoti <amzoti at gmail.com>
  • Date: Fri, 7 Feb 2014 08:08:27 -0500 (EST)
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  • References: <20140201055416.D6FE16A13@smc.vnet.net> <lckifh$1gr$1@smc.vnet.net>

On Saturday, February 1, 2014 8:44:33 PM UTC-8, Bob Hanlon wrote:
> The step-by-step solution provides the result for t >= 0
> 
> 
> 
> 
> 
> sol = ((WolframAlpha[
> 
>        "v''+10 v'+125 v=250 unitstep(t),v(0)=0,v'(0)=25",
> 
>        {{"DifferentialEquationSolution", 1}, "Output"}] //
> 
>       ReleaseHold)[[1]]) // ToRules
> 
> 
> 
> 
> 
> {v[t] -> ((5/2)*Sin[10*t])/E^(5*t) +
> 
>        (((-(5/2))*Sin[10*t])/E^(5*t) +
> 
>             ((1/2)*(4*E^(5*t) - 4*Cos[10*t] + 3*Sin[10*t]))/
> 
>               E^(5*t))*UnitStep[t]}
> 
> 
> 
> 
> 
> 
> 
> Simplify[sol, t >= 0]
> 
> 
> 
> 
> 
> {v[t] -> 2 - (2*Cos[10*t])/E^(5*t) +
> 
>        ((3/2)*Sin[10*t])/E^(5*t)}
> 
> 
> 
> 
> 
> 
> 
> Bob Hanlon
> 
> 
> 
> 
> 
> On Sat, Feb 1, 2014 at 12:54 AM, amzoti <amzoti at gmail.com> wrote:
> 
> 
> 
> > When you solve this DEW using WA, you get a result.
> 
> >
> 
> > However, when you click step-by-step, the result is different.
> 
> >
> 
> > Is this a bug?
> 
> >
> 
> > v'' + 10 v' + 125 v = 250 unitstep(t), v(0) = 0, v'(0) = 25
> 
> >
> 
> > Thanks
> 
> >
> 
> >

Thanks all!

Bob Hanlon: I see that you reply to many posting with excellent feedback.

I have always wondered (as your posts are different than many in a very good way), how did you learn Mathematica so well?

What approach and/or references did you use?

Regards -A



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