"Chambers" <bdc### [at] yahoocom> wrote:

> The original function is f(x) = M*R*(D^x), where M, R and D are constants.
>
> I'd be using the function g(A) = sum of f(x), where x=0..A

If x is just integers from zero to a, then each term differs by an additional
factor of D.  Then you have the sum of a geometric series,

sum_{x=0...A} ( M*R*(D^x) )   =   M*R*(1-D^(A+1)) / (1-D).

This looks much nicer on the wikipedia page,
http://en.wikipedia.org/wiki/Geometric_progression .  Correct me if I'm
misinterpreting, but this should give you the summation in a single expression.

 - Ricky

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