A=4/1.2+4/2.3+4/3.4+……..+4/2020.2021

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1. `A= 4/1.2 + 4/2.3 + 4/3.4 +….+ 4/2020.2021`

   `A = 4( 1/1.2 + 1/2.3 + 1/3.4 +….+ 1/2020.2021)`

   `A= 4( 1/1 -1/2 + 1/2 -1/3 + 1/3 -1/4 +…+ 1/2020- 1/2021)`

   `A = 4(1 – 1/2021)`

   `A = 4. 2020/2021`

   `A= 8080/2021`

   Vậy `A= 8080/2021`

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2. `A=4/(1.2)+4/(2.3)+4/(3.4)+……..+4/(2020.2021)`

   `A = 4 . (1/(1.2)+1/(2.3)+1/(3.4)+……..+1/(2020.2021))`

   `A = 4 . (1-1/2+1/2-1/3+1/3-1/4+…..+1/2020-1/2021)`

   `A = 4 . (1-1/2021)`

   `A = 4 . 2020/2021`

   `A = 8080/2021`

   (Chúc bạn học tốt)

    

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