Trang 694 11.2 21-34.Determine whether the series is convergent or divergent. If it is convergent,
find its sum.

21.
1
 2n
n 1

22.
n 1
 2n  3
n 1

k2
23.  2
k 2 k  1

24.
k (k  2)
 (k  3)
k 1
2
1  2n

n
n 1 3

25.
11.8 3-28. Find the radius of convergence and interval of convergence of the series.

3.

n 1
xn
n
4.
(1)n x n

n 1
n 0
5.
(1)n1 x n

n3
n 0



6.

nx n
n 1

7.
xn

n 1 n !