1×1/3+1/3×1/5+1/5×1/7+1/7×1/9+……+1/99×1/101

1×1/3+1/3×1/5+1/5×1/7+1/7×1/9+……+1/99×1/101
1×1/3+1/3×1/5+1/5×1/7+1/7×1/9+……+1/99×1/101

1×1/3+1/3×1/5+1/5×1/7+1/7×1/9+……+1/99×1/101
总结这题就是 1/n×1/(n+2)的问题
1/n×1/(n+2)
=1/2×[1/n-1/(n+2)]
接下来就是相加了
自己试着写几个就好了