Bài 14: 

a) A = 1.2 + 1/2.3 + 1/3.4 + ... + 1/98 .99 + 1/99 . 100 

b) B = 1/5.6 + 1/6.7 + ... + 1/24 . 25

c) C = 2/1.3 + 2/3.5 + 2/5.7 + ... + 2/99 . 101

d) D = 5^2/1.6 + 5^2/6.11 + ... + 5^2/26.31

e) E = 4/11 . 16 + 4/16 . 21 + 4/21 . 26 + ... + 4/61.66

q) Q= -5/99 .97 - 5/97.95 - 5/95.93 - ... - 5/7.5 - 5/5.3 - 5/3.1