Excel for Mac 2011: goal seek function produces bizarre output, what's wrong?

When you hand enter 9.17% into i, do g or f go to 0? When I entered everything as you described, 9.17% in i did not make g or f 0. The value of -3.2E14 did make f 0, so it is kind of a correct solution for a "root" of f. Though, looking at the equation in f, f will approach 0 asymptotically as i approaches negative infinity (and as i approaches positive infinity).

I added a spreadsheet that shows how I would analyze this sort of problem. I add a range where I can calculate my "objective function" (g in this case) against several values of my "independent variable (i in this case). As expected, the graphs shows an asymptote at 0.0439, and it shows the root just below 0.1. I calculate a root where i=0.087.

I don't know what you did wrong. Perhaps you tried to set f=0 instead of g. Or perhaps you gave it a horrible "initial guess" and goal seek diverged instead of converging.

Since goal seek uses the Newton Raphson method, I might suggest that you review how this algorithm works. I like this tutorial http://www.cs.utah.edu/~zachary/isp/...ot/Newton.html You might also find my Newton-Raphson tutorial that does not use goal seek interesting (or confusing) http://www.excelforum.com/tips-and-t...ind-roots.html