`-(-1)/21 - 1/28`
`=1/21-1/28`
`=4/84 - 3/84`
`=(4-3)/84`
`=1/84`
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`-(-1)/21 - 1/28`
`=1/21-1/28`
`=4/84 - 3/84`
`=(4-3)/84`
`=1/84`
D=(1-1/21)(1-1/28)...(1-1/1326)
B=1/15+1/21=1/28+......+1/190
F= 1/21+1/28+1/36+1/45+...+1/66
1\21+1\28+1\36+...+1\x(x+1)=1\9
Tính: (1-1/21)(1-1/28)(1-1/36)...(1-1/120)
A = (1- 1/21)(1 - 1/28)(1 - 1/36)...(1 - 1/1326)
A=(1-1/21).(1-1/28).(1-1/36)....(1-1/1326) = ?
tính 1/15+1/21+1/28+...+1/190
Tính tổng C = 1/15 + 1/21 + 1/28 +...+ 1/190
tính S=1/10+1/15+1/21+1/28+.....+1/120