1/6+1/12+1/20+...+1/72
=1/2.3+1/3.4+1/4.5+...+1/8.9
=1/2-1/3+1/3-1/4+1/4-1/5+...+1/8-1/9
=1/2-1/9
=7/18
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Tính B=1/96-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/12
1/6+1/12+1/20+1/30+1/42+1/56+1/72
A= 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90
1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2 = ?
8/9 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
Tính : B=1/90-1/72-1/56-1/42-1/30-1/20-1/6-1/12
A = 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110=?
S=1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110
9/10-1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2 = ?