1/1x3+1/3x5+1/5x7+1/7x9+1/9x11+1/11x13=

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1/1x3+1/3x5+1/5x7+1/7x9+1/9x11+1/11x13=
1/1x3+1/3x5+1/5x7+1/7x9+1/9x11+1/11x13=

1/1x3+1/3x5+1/5x7+1/7x9+1/9x11+1/11x13=
1/1x3 = （1-1/3)/2
1/3x5 = (1/3-1/5)/2
.
.
.
1/11x13 = (1/11-1/13)/2
以上各式累加
原式=（1-1/13）/2=6/13