BÀi này dễ thôi bạn ạ
N=3(1/5.7+1/7.9+.........+1/197.199)
N=3/2( 1/5-1/7+1/7-1/9+1/9-..........+1/197-1/199)
N=3/2(1/5-1/199)
N=3/2.194/995
N=291/995
k đúng cho mình nhé
N=3.1/2.(1/5-1/7+1/7-1/9+1/9-1/11+...+1/197-1/199)
N=3.1/2.(1/5-1/99)
N=3.1/2.94/495
N=3.47/495
N=47/165
N=3/5.7+3/7.9+........+3/197.199
=>N=3/2(2/5.7+2/7.9+.....+2/197.199)
=>N=3/2(1/5-1/7+1/7-1/9+........+1/197-1/199)
=>N=3/2(1/5-1/199)
=>N=3/2x194/995=291/995