a, Tìm tất cả các cặp số nguyên (x,y) thỏa mãn: x/2- 2/y=1/2

b,Tinh hợp lí: A=(1/2+1/12+1/30+...+1/9900) : (-6/51- 6/52- 6/53-...- 6/100)

a=(\(\dfrac{1}{2}+\dfrac{1}{12}+\dfrac{1}{30}+...+\dfrac{1}{9900}\)):(\(\dfrac{-6}{51}-\dfrac{6}{52}-\dfrac{6}{53}-...-\dfrac{6}{100}\))

giúp mik giải nhé 

cảm ơn !

Cho A=1/51+1/52+1/53+...+1/100 và B=1/2+1/12+1/30+...+1/9900.

Tính A-B

Cho A=1/51+1/52+1/53+...+1/100

Cho B=1/2+1/12+1/30+...+1/9900

Tính A-B

1/2+1/12+1/30+...+1/9120+1/9506+1/9900. / 50-50/51-51/52-...-97/98-98/99-99/100

Cho S = 1/51 + 1/52 + 1/53 + ... + 1/100 . CMR 7/12 < S < 5/6

chung minh rang

1/2<1/51+1/52+1/53+.....1/100<1

7/12<1/21+1/22+....1/40<5/6

tính c=1/1*2+1/3*4+1/5*6+...+1/99*100

tính b=1/51+1/52+1/53+...+1/100

2/3*x-(1/2-3/4+5/6-7/8+...+197/198-199/200)=1/51+1/52+1/53+...+1/99+1/100

Tìm x