Why is it necessary to use a negative present value when solving for N (the number of

Question:

Why is it necessary to use a negative present value when solving for N (the number of payments) or I/Y (the rate of return)? Similarly, why does the answer have a negative sign if positive payments were used when solving for a on a calculator?
Future Value
Future value (FV) is the value of a current asset at a future date based on an assumed rate of growth. The future value (FV) is important to investors and financial planners as they use it to estimate how much an investment made today will be worth...