2019/1.5+2019/5.9+2019/9.13+….+2019/2017.2021

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1.    `2019/(1.5)+2019/(5.9)+2019/(9.13)+….+2019/(2017.2021)`

   `= 2019(1/(1.5)+1/(5.9)+1/(9.13)+….+1/(2017.2021))`

   `= 2019.1/4.(4/(1.5)+4/(5.9)+4/(9.13)+….+4/(2017.2021))`

   `= 2019/4(1-1/5+1/5-1/9+…+1/2017-1/2021)`

   `= 2019/4.(1-1/2021)`

   `= 2019/4.2020/2021`

   `= 4078380/8084=1019595/2021`

    

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2. Giải thích các bước giải:

   `2019/(1.5) +2019/(5.9) +2019/(9.13) +…+2019/(2017.2021)`

   `= 2019.(1/(1.5) +1/(5.9) +1/(9/13) +…+1/(2017.2021))`

   `= (2019/4).(4/(1.5) +4/(5.9) +4/(9/13) +…+4/(2017.2021))`

   `= (2019/4).(1 -1/5 +1/5 -1/9 +1/9 -1/13 +…+1/2017 -1/2021)`

   `= (2019/4).(1 -1/2021)`

   `= (2019/4).(2020/2021)`

   `= (2019.2020)/(4.2021) = (2019.505)/2021 = 1019595/2021`

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