1/1x4+1/4x7+……+1/91x94=?
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1/1x4+1/4x7+……+1/91x94=?1/1x4+1/4x7+……+1/91x94=?1/1x4+1/4x7+……+1/91x94=?1/1x4=(1/3)*(1/1-1/4)1/4*7=(
1/1x4+1/4x7+……+1/91x94=?
1/1x4+1/4x7+……+1/91x94=?
1/1x4+1/4x7+……+1/91x94=?
1/1x4=(1/3)*(1/1-1/4)
1/4*7=(1/3)(1/4-1/7)
..
1/91*94=(1/3)(1/91-1/94)
所以：
1/1x4+1/4x7+……+1/91x94
＝（1/3)*(1/1-1/4+1/4-1/7+..+1/91-1/94)
=(1/3)(1-1/94)
=31/94
采用裂项法
原式=1/3(1/1-1/4+1/4-1/7++1/91-1/94)=31/94
1/1x4+1/4x7+…+1/97x100
1/1x4+1/4x7+……+1/91x94=?
1/1x4 + 1/4x7 + 1/7x10 +…+ 1/91x94=?
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1/1x4+1/4x7+1/7x10+……+1/97x100SOS!SOS!
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