CHO N1, N N N NA, CMR
Câu 4:
Cho N
1, n N
n n
a, CMR: 1+ 2+ 3+....+n =
(
1)
2
n n
n
b, CMR: 1
2
+2
2
+ 3
2
+...+n
2
=
(
1)(2
1)
6
Câu 4:
Cho N
1, n N
n n
a, CMR: 1+ 2+ 3+....+n =
(
1)
2
n n
n
b, CMR: 1
2
+2
2
+ 3
2
+...+n
2
=
(
1)(2
1)
6