This problem is easier than you think. The series doesn't alternate (it will always be positive - you can figure out why on your own). The function f(n) also aproaches zero, as n tends to infinity as the numerator will always be a number between 1 and 0 (there maybe some fluctuation - but you are approaching zero). You can use the comparison test, and notice that the similar function is 1/2^n (which is convergent).