If n is an integer, f(n) = f(n-1) - n and f(4)=13. What is the value of f(6)?
Choose the correct choice
A) - 1  B) 0  C) 1  D) 2  E) 4

Rationale: "since f ( n ) = f ( n - 1 ) - n then : f ( 6 ) = f ( 5 ) - 6 and f ( 5 ) = f ( 4 ) - 5 . as given that f ( 4 ) = 13 then f ( 5 ) = 13 - 5 = 8 - - > substitute the value of f ( 5 ) back into the first equation : f ( 6 ) = f ( 5 ) - 6 = 8 - 6 = 2 . answer : d . questions on funtions to practice :"
Answer: D