If you would like to know the value of f(4), you can calculate this using the following steps:
f(n) = 1/2 * f(n-1) + 2
f(1) = 8
f(2) = 1/2 * f(2-1) + 2 = 1/2 * f(1) + 2 = 1/2 * 8 + 2 = 4 + 2 = 6
f(3) = 1/2 * f(3-1) + 2 = 1/2 * f(2) + 2 = 1/2 * 6 + 2 = 3 + 2 = 5
f(4) = 1/2 * f(4-1) + 2 = 1/2 * f(3) + 2 = 1/2 * 5 + 2 = 5/2 + 2 = 5/2 + 4/2 = 9/2 = 4 1/2
The correct result would be 4 1/2.