Question 984615
A good way could be to linearize the equation model, and then plot points on graph paper, and find your best line.  Your points need to be  (n, log((A)) ), for whichever log base you want to use.  Horizontal axis coordinate is for n, and vertical axis coordinate is for log((A)).  You would then find the parts of your equation directly reading the graph.  You have several points to plot, so hopefully this may be enough to find an easy or reliable line.


Taking log of each side of your basic model:


{{{log((A))=log((P))+log(((1-r)^n))}}}


{{{log((A))=n*log(((1-r)))+log((P))}}}


The slope will be  {{{log((1-r))}}}, and the vertical axis intercept will be {{{log((P))}}}.