2/15+2/35+2/63+.+2/323=

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2/15+2/35+2/63+.+2/323=
2/15+2/35+2/63+.+2/323=

2/15+2/35+2/63+.+2/323=
2/15+2/35+2/63+.+2/323
=1/3-1/5+1/5-1/7+1/7-1/9+.+1/15-1/17+1/17-1/19
=1/3-1/19
=(19-3)/3*19
=16/57

原式等于1/3-1/5 1/5-1/7 1/7........ 1/17-1/19=1/3-1/19

= (1/3 - 1/5) +(1/5 - 1/7) + (1/7 - 1/9) + . + (1/17 - 1/19)
= 1/3 -1/19
= 16/57

15=4^2-1 35=6^2-1 原式=2/(4-1)*(4+1)+2/(6-1)*(6+1)+...+2/(18-1)*(18+1)=1/3-1/19