If f(n) = -2f(n-1), and you need to evaluate f(5), then we need to look at the the function like this.
f(5) = -2f(4)
f(4) = -2f(3)
f(3) = -2f(2)
f(2) = -2f(1)
Now, let's work this from the bottom up
f(2) = -2f(1) = -2(3) = -6 since we are told that f(1) = 3
f(3) = -2f(2) = -2(-6) = 12
f(4) = -2f(3) = -2(12) =-24
f(5) = -2f(4) = -2(-24) = 48
Hope this helps.
