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Topic: Solving equation
Replies: 3   Last Post: Apr 7, 2008 12:10 PM

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Walter Roberson

Posts: 5,173
Registered: 2/26/06
Re: Solving equation
Posted: Apr 4, 2008 6:12 PM
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In article <ft67km$agj$1@fred.mathworks.com>,
Wouter Geelen <wouser_geelen@hotmail.com> wrote:

>I tried to do this myself but I can't get it done. I got
>the following equation.


>Ti = -1200*exp(-1/7200*t)+1200

>Now I want to solve this function for Ti = 1080. So what I
>want to find is t. How do I do that :?


Ti = -1200*exp(-1/7200*t)+1200, so
Ti - 1200 = -1200 * exp(-t/7200), so
(1200 - Ti)/1200 = exp(-t/7200), so
ln((1200 - Ti)/1200) = -t/7200, so
-ln(1200/(1200-Ti)) = -t/7200, so
t = 7200 * ln(1200/(1200-Ti))

Substituting in Ti = 1080, we get the result 7200 * ln(10)
which is about 16578.61267.

--
"Is there any thing whereof it may be said, See, this is new? It hath
been already of old time, which was before us." -- Ecclesiastes



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