The monthly mortgage payment in dollars, P, for a house is a function of three variables:

P = f(A, r,N),

where A is the amount borrowed in dollars, r is the interest rate, and N is the number of years before the mortgage is paid off.
(a) f(92000, 14, 30) = 1090.08. What does this tell you, in financial terms?

(b) ∂P/∂r|_{(92000,14,30)} = 72.82. What is the financial significance of the number 72.82?
(c) Would you expect )P ∕)A to be positive or negative? Why?
(d) Would you expect )P ∕)N to be positive or negative? Why?