" wrote:
I'm trying to figure out the math equations for Present Value, Future
Value, and Payment in Excel.

I cannot say for sure what Excel does. But the typical formula is:

0 = PV + (1 + i*TYPE)*PMT*( (1 - (1+i)^(-n)) / i ) + FV*(1+i)^(-n)

Solve for PV, FV or PMT. Solve for i iteratively.