Đáp án:
Giải thích các bước giải:
`A = 1/1.2 + 1/3.4 +.......+ 1/99.100`
`A = 1 - 1/2 + 1/3 - 1/4 +.......+ 1/99 - 1/100`
`A = ( 1 + 1/3 +..........+ 1/99 ) - ( 1/2 + 1/4 +.......+ 1/100 )`
`A = ( 1 + 1/2 + 1/3 +........+ 1/99 + 1/100 ) - 2 . ( 1/2 + 1/4 +.....+ 1/100 )`
`A = ( 1 + 1/2 + 1/3 +........+ 1/99 + 1/100 ) - ( 1 + 1/2 +.......+ 1/50 )`
`A = 1/51 + 1/52 +.......+ 1/100`
-Ta có: `B = 2021/51 + 2021/52 +......+ 2021/100`
`-> B = 2021 . ( 1/51 + 1/52 +.....+ 1/100 )`
`-> B/A = (2021 . ( 1/51 + 1/52 +.....+ 1/100) )/(1/51 + 1/52 +.......+ 1/100)`
`-> B/A = 2021 ( TM )`
