# Exponential Growth Functions

I have a worksheet of about 24 problems and it seems to be split by two different sorts. I'm wondering if one could walk me through two so I can finish the worksheet on my own.

Write the exponential function y=20e^-0.04t in the form y=ab^t.

Find b accurate to 5 decimal places.


The second type of questions on the worksheet is in the following format.

Write the exponential function P=721(0.98)^t in the form P=ae^kt .


Thank you in advance to anyone that can point me in the right direction

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$$\large (a^b)^c=a^{(b\cdot c)}$$ – anon Sep 21 '11 at 6:36

There is one thing you should know to do your homework and it is the following formula $$e^{a\cdot\ln b} = b^a.$$ For example, if you have to write function $P = (0.555)^t$ in the form $P = e^{kt}$, then directly from the above formula you will get $$(0.555)^t = e^{t\cdot \ln(0.555)}.$$ P.S. If you need to find $e^x$ with some accuracy, then it would be useful to represent $e^x$ as a series.
$$y=20e^{-0.04t} = 20 {\huge(}e^{-0.04}{\huge)}^t = ab^t\qquad\text{where }a=20\text{ and }b= e^{-0.04}.$$