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`
