Tính A= (1-1/2).(1-1/3).(1-1/4)...(1-1/2020).(1-1/2021)

Đáp án+Giải thích các bước giải:

`A= (1-1/2).(1-1/3).(1-1/4)...(1-1/2020).(1-1/2021)`
`A= (2/2-1/2).(3/3-1/3).(4/4-1/4)...(2020/2020-1/2020).(2021/2021-1/2021)`
`A=1/2. 2/3. 3/4.... 2019/2020. 2020/2021`
`A=[1.2.3....2019.2020]/[2.3.4....2020.2021]`
`A=[1.cancel[2].cancel[3]....cancel[2019].cancel[2020]]/[cancel[2].cancel[3].cancel[4]....cancel[2020].2021]`
`A=1/2021`
Vậy `A=1/2021`