Goal Seek - Why make the PV negative?

[Guest]

I'm using goal seek on the following data to find the Term (in years) if the
Monthly Repayment is 2000 on a loan. The only way I can get goal seek to
find the correct answer (19.56536985 years) is to make the PV negative (-B6)
in the PMT formula. The PMT formula in cell B10 is =PMT(B7/12,B8*12,-B6).
Can somone explain why the PV has to be negative? I'm not the most
mathematically-minded person.
A B
3 Purchase Price 250000
4 Purchase Costs 11500
5 Deposit 50000
6 Loan Amount 211500
7 Interest Rate 9.60%
8 Term (in years) 30

10 Monthly Repayment 1794

 

[Guest]

Excel uses a cash in cash out method.

If you borrow 100,000 then you owe 750 a month .. ie -750

Good luck