作业帮1/3+1/15+1/35+1/63+1/99 用裂项法.
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1/3+1/15+1/35+1/63+1/99 用裂项法.
1/3+1/15+1/35+1/63+1/99 用裂项法.
1/3+1/15+1/35+1/63+1/99 用裂项法.
1/3+1/15+1/35+1/63+1/99
=1/(1*3)+1/(3*5)+1/(5*7)+1/(7*9)+1/(9*11)
=1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11
=1-1/11
=10/11
1/3+1/15+1/35+1/63+1/99
=1/2*（1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=1/2*(1-1/11)
=1/2*10/11
=5/11