Bài 1 : Tính nhanh
A= ( 1/2 - 1 ) . (1/3 - 1 ) . ( 1/4 - 1) .... ( 1/99 -1)
B= -7/4 . ( 33/12 + 3333/2020 + 333333/202020 + 3333/ 4242 )
C= ( 1 + 1/2) . ( 1 + 1/3) . ( 1+ 1/4) .... (1+ 1/99)
D= ( 1- 1/2 ) . ( 1- 1/3 ) . ( 1- 1/4 ) .... ( 1- 1/99)