If n is an integer, f(n) = f(n-1) - n and f(4)=20. What is the value of f(6)? Choose the correct answer:
A) 9 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)=20 then f(5)=20-5= 
<gadget id="calculator">20-5</gadget>
<output>15</output>
15 --&gt; substitute the value of f(5) back into the first equation: f(6)=f(5)-6=15-6= 
<gadget id="calculator">15-6</gadget>
<output>9</output>
9.   Answer: A.   Questions on funtions to practice:
<result>A</result>
If n is an integer, f(n) = f(n-1) - n and f(4)=20. What is the value of f(6)?