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2008-03-07 23:32:28
Blehm98
conservative hatemonger
+150|6944|meh-land
K, so a few days ago i had a math test, and i seriously could not get one of the free response questions...
I'll only post the hard stuff, but yeah...
halps?

S(t)=rate of something that i forgot

S(t)=Ce^(kt)
S(1)=6=Ce^(k)
every time t increases by 5, the value of the rate doubles, so S(5) = 2S(1)
or S(5)=12=Ce^(5k)=2Ce^(k)

i need to find C and k

i seriously spent like half an hour trying to get this one, and it was the only part of the free response i had any trouble with... 
i know there's an easy way to do it too, i just don't know how...

so halps?
2008-03-07 23:55:35
Blehm98
conservative hatemonger
+150|6944|meh-land
no AIDS?

well when i get up tomorrow i shall hope someone has replied with the answer and how to reach it, because i really want to know how to do it

and don't feel like waiting for my teacher to show me how to do it monday
2008-03-08 00:17:44
-TL-
Srs lurker
+25|6973|Oklahoma City
I worked the problem out below, but I think I did something wrong, and I'm too tired to see it now.
Maybe some Aussie or Euro has a clearer mind?

given
6 = Cek
12 = Ce5k

then
6 / ek = C
  12 = (6 / ek)e5k
   12 = 6e4k
    2 = e4k
    ln(2) = 4k
    k = ln(2) / 4
     
k = 0.1733
C = 6 / e0.1733
 
C = 5.0453
Amirite?

Last edited by -TL- (2008-03-08 00:33:26)

2008-03-08 09:36:23
Blehm98
conservative hatemonger
+150|6944|meh-land
hmmm
i worked it all out but screwed up on the k somehow

i must have accidentally screwed up a minor step, because i think i got C =  to something around 5 but i got k negative...

ah well

 

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