S 1 2C 1N2 C2 2N 2 C3 3N
Câu 50.Tính tổng:
S 1 2C
1
n
2 C
2
2
n
2 C
3
3
n
... ( 1) 2 C
n n
n
n
a/1
n
b/( 2)
n
c/( 3)
n
d/( 1)
n
S 1 2C
1
n
2 C
2
2
n
2 C
3
3
n
... ( 1) 2 C
n n
n
n
a/1
n
b/( 2)
n
c/( 3)
n
d/( 1)
n