Chứng tỏ rằng: a)
1
1.2
+
1
2.3
+
...
+
1
9.10
<
1
b)
3
2.5
+
3
5.8
+
3
8.11
+
3
11.14
+
3
14.17
+
3
17.20
<
1
2
c)
1
2
2
+
1
3
2
+
1
4
2
+
...
+
1
25
2
<
1
...
Đọc tiếp
Chứng tỏ rằng:
a) 1 1.2 + 1 2.3 + ... + 1 9.10 < 1
b) 3 2.5 + 3 5.8 + 3 8.11 + 3 11.14 + 3 14.17 + 3 17.20 < 1 2
c) 1 2 2 + 1 3 2 + 1 4 2 + ... + 1 25 2 < 1
a ) 1 1.2 + 1 2.3 + ... + 1 9.10 = 9 10 < 1.
b ) 3 2.5 + 3 5.8 + 3 8.11 + 3 11.14 + 3 14.17 + 3 17.20 = 1 2 − 1 20 < 1 2 .
c ) T a c ó 1 2 2 < 1 1.2 ; 1 3 2 < 1 2.3 ; 1 4 2 < 1 3.4 ; ... ; 1 25 2 < 1 24.25 .
D o đ ó , 1 2 2 + 1 3 2 + 1 4 2 + 1 25 2 < 1 1.2 + 1 2.3 + 1 3.4 + ... + 1 24.25 < 1.