Asequence is defined by the recursive formula f(n+1)=f(n)-2. if f(1)=18,what is f(5)?

To find f(5), you need to know f(4), to know f(4), you need to find f(3), to know f(3), you need to know f(2)
Use the recursive formula f(n+1)=f(n)-2,
f(2)=f(1)-2, and f(1)=18 is given, so f(2)=18-2=16
f(3)=f(2)-2=16-2=14
f(4)=12
f(5)=10

another way to do it is using the formula: the nth term=the first term +d(n-1)
d represents the difference, which is -2 in this case
so f(5)=f(1)-2(5-1)
f(5)=18-8=10