1/3+1/15+1/35+1/63

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1/3+1/15+1/35+1/631/3+1/15+1/35+1/631/3+1/15+1/35+1/631/3+1/(3*5)+1/(5*7)+1/(7*9)=1/3+1/2*(1/3-1/5)+

1/3+1/15+1/35+1/63
1/3+1/15+1/35+1/63

1/3+1/15+1/35+1/63
1/3+1/(3*5)+1/(5*7)+1/(7*9)=1/3+1/2*(1/3-1/5)+1/2(1/5-1/7)+1/2(1/7-1/9)消去同等的数整理可得原式=1/3+1/6-1/18=4/9