If n is an integer, f(n) = f(n-1) - n and f(4)=13. What is the value of f(6)?  Options:
A) -1  B) 0  C) 1  D) 2  E) 4
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= 
<gadget id="calculator">13-5</gadget>
<output>8</output>
8 --&gt; substitute the value of f(5) back into the first equation: f(6)=f(5)-6=8-6= 
<gadget id="calculator">8-6</gadget>
<output>2</output>
2.   Answer: D.   Questions on funtions to practice:
<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)?