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2/15+2/35+2/63+2/99+2/143+2/195=()
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2/15+2/35+2/63+2/99+2/143+2/195=( )
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答案和解析
2/15+2/35+2/63+2/99+2/143+2/195
=2×(1/15+1/35+1/63+1/99+1/143+1/195)
=2×（1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15）
=2×(1/3-1/15)
=8/15
=2×(1/15+1/35+1/63+1/99+1/143+1/195)
=2×（1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15）
=2×(1/3-1/15)
=8/15
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