Find a formula for the nth partial sum of the series and use it to determine if the series converges or diverges. If the series converges, find its sum. E 3 cos n + 5 - cos n+6 n = 1 Sn (Type an exact answer, using it as needed.) If the series converges, what is its sum? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. The sum of the series is (Type an exact answer, using it as needed.) O B. The series diverges