Question

[Huyền Nguyễn]

1. Tính tổng 

a, A=1/2.3 + 1/3.4 + ... + 1/99.100

b, B= 5/1.4 + 5/4.7 + ... + 5/100.103

c, C= 1/15 +1/35 + ... + 1/2499

d, D=1/1.6 + 1/6.11 + 1/11.16 + ... +1/(5n+1).(5n+6)

mn ơi mình đang cần gấp

Answer 1

[Nguyễn Lê Phước Thịnh]

a: =1/2-1/3+1/3-1/4+...+1/99-1/100

=1/2-1/100=49/100

b; =5/3(1-1/4+1/4-1/7+...+1/100-1/103)

=5/3*102/103

=510/309=170/103

c: =1/2(1/3-1/5+1/5-1/7+...+1/49-1/51)

=1/2*16/51=8/51