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

• To: mathgroup at smc.vnet.net
• Subject: [mg132291] Re: Result to DEQ with WA versus Step-by-Step Yields
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Sat, 1 Feb 2014 23:54:36 -0500 (EST)
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• References: <20140201055416.D6FE16A13@smc.vnet.net>

```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
>
>

```

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