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Mathematics 8 Online
darkknight:

what is the practical significance of the number 200 in the equation: (200(1-.956e^(-.18t)))

darkknight:

the y values only make it to 200 but why?

justjm:

\(\lim_{t\to\infty}200\left(1-.956e^{-.18x}\right)\) = 200 So the function can never go past 200

darkknight:

im confused still

darkknight:

how do you know that?

justjm:

Sure let me explain \(\lim_{t\to\infty}200\left(1-.956e^{-.18x}\right)\) =\(lim_{t\to\infty}200\left(1-\frac{.956}{e^{.18t}}\right)\) As t approaches infinity, the denominator with e^.18t gets larger, so the term is 1/∞, which = 0 \(lim_{t\to\infty}200(1-0)=200\)

darkknight:

why did you do step 2, I mean why did you take (1−.956e^−.18t) and do (1−(.956/e^.18t))?

justjm:

Exponent rules...a negative power on a variable means that it's going in the denominator \( x^{-n} = \frac{1}{x^n}\)

darkknight:

oh, didn't see that

darkknight:

one more thing

darkknight:

whats this last thing As t approaches infinity, the denominator with e^.18t gets larger, so the term is 1/∞, which = 0 limt→∞200(1−0)=200

darkknight:

I get this As t approaches infinity, the denominator with e^.18t gets larger,

justjm:

So think of it this way. 1/∞ means you have fractions getting smaller and smaller..closer to 0. You have 1/2, then 1/4, then 1/200, then 1/10000000. It's approaching 0, right? So the LIMIT of 1/∞ is 0

darkknight:

ok

darkknight:

oh, cuz it gets infinitely smaller

justjm:

The e^.18t is getting larger, meaning that the denominator is getting larger...towards infinity. It looks like 1/∞ now. So when we take the LIMIT of that, we're going to get 0.

darkknight:

okay, I understand now

darkknight:

you are a genius

justjm:

Tyty I try :)

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