Đáp án:
Giải thích các bước giải:
A = 4 /11.16 + 4/16.21 + 4/21.26 + .... + 4/61.66
= 4/ 5 . ( 1/11 - 1/16 + 1/16 - 1/21 + 1/21 - 1/26 + .... + 1/61 - 1/66
= 4/5 . ( 1/11 - 1/66)
= 4/5 . ( 6/66 - 1/66)
= 4/5 . 5/66
= 20/330
= 2/33
A = 3/2.4 + 3/4.6 + 3/6.8 + ... + 3/2000.2004
= 3/2 . ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + ... + 1/2000 - 1/2004
= 3/2 . ( 1/2 - 1/2004)
= 3/2 . ( 1002/2004 - 1/2004)
= 3/2 . 1001/2004
= 3003/4008
= 1001/1336
Vậy: A < 1001
5
158
2
Còn câu C nữa ạh