Math help appreciated

Frostweave · Post by **Frostweave** » Tue May 09, 2006 3:32 pm

I can't for the life of me remember how to do natural log. I believe that's how you solve problems with e to some power. Anyways, here is the problem. It is from a section in my math book about surge functions. Any help would be greatly appreciated. I'm trying to finish all my homework in this class before it is due and this is the only assignment that's got me stuck.

If t is in hours, the drug concentration curve for a drug is given by C = 17.2te(to the, i.e.power) -0.4t ng/ml. The minimum effective concentration is 10 ng/ml.
If the second dose of the drug is to be administered when the first dose becomes ineffective when should the second dose be given.

Thanks in advance!
Frost

Schythe · Post by **Schythe** » Tue May 09, 2006 11:58 pm

I had this equation a couple weeks ago. need to enter the equation in a graphing calculator and then on the second y digit enter the 10 ng/ml. where they intercept is where you should give the second dose from what i understand. if all else fails look in the back of the book and reverse engineer the problem (i tend to do that every once in a while) Don't just write the answer down as it can come back to haunt you when the question is asked later.

Ancient Schythe Gravestalker
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Frostweave · Post by **Frostweave** » Fri May 12, 2006 11:07 am

Thank you for the help Schythe. I'm wondering if we have the same book. The author is assuming we all have a graphing calculator to punch the problem in (my professor confirmed that this week.) What's lame is the class doesn't require a graphing calculator and mine bit the dust and since I'm graduating in 4 weeks I see no need to buy another for one course.

Had to do a guess and check table if you remember those. Thank you again though!!

Toag · Post by **Toag** » Fri May 12, 2006 11:21 am

is the equation

C=17.2 *t*e^(-.4*t)
or
C=17.2*e^(-.4*t)

where the ^ indicates rasing to a power

Schythe · Post by **Schythe** » Sun May 14, 2006 5:38 pm

it is the C= 17.2*t*e^(-.4*t)

Aye same thing happend to me frost. i had a ti83+ silver edition but i found out over the course of the year that i didn't use it that it's screen is messed up and can't graph because i miss half the pixles and they add up and make it more confusing. i borrowed a friends calc till he said he needed it for his kid a few days before my midterm =( so i went and got a Ti 89 titanium. that thing was so confusing all the butens are different and it looks more like a pda with all the applications when i first turned it on. but it can solve equations and do everything once i figured it out. but i didn't have to much luck as i was opening the package for it as she passed out the tests lol.

Ancient Schythe Gravestalker
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Feemee · Post by **Feemee** » Sun May 14, 2006 11:35 pm

Can use GCalc free online graphics calculator:

http://www.esjc.cc.al.us/divisions/mat_div/gcalc.htm

Enter 17.2 *x*e^(-.4*x) as the formula (should come out around 5.71 hours).