stuck on a diff eq problem

recipro · #1 09-13-2007, 06:36 PM

Let 10pm be time X. Then 11pm is time X+1...
31 = 22e^(kx) + 15 ...
16/22 = e^(kx) ...
ln (8/11) = kx
k = ln (8/11) / x

Now, plug in x+1...
29 = 22e^(kx+k) + 15 ...
14/22 = e^(kx+k)
ln (7/11) = k (x+1)
ln (7/11) = ln (8/11) * (1 + 1/x)

I don't feel like doing the rest, but solve for x obv.

djk123 · #2 09-13-2007, 07:41 PM

Thank you that was easy enough. I actually ended up doing it a different way. Someone else suggested doing T=31 as t(0) and t(1)=29. I got -2.38486 instead of 2.38486 from your method, but the negative doesnt matter i guess. so i guess the answer is 7:37:05 PM.

TheSalche · #3 09-14-2007, 12:54 AM

Do you go to UIUC? I swear I had that problem in my ME 340 class ...

djk123 · #4 09-14-2007, 01:19 AM

[ QUOTE ]
Do you go to UIUC? I swear I had that problem in my ME 340 class ...

[/ QUOTE ]

no villanova