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
<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">13 - 5</gadget>
<output>8</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<result>D</result>
if n is an integer, f ( n ) = f ( n - 1 ) - n and f ( 4 ) = 13. what is the value of f ( 6 )?
subtract(subtract(13, add(1, 4)), 6)
"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 :"