用 错位相减法求：1\2-1\4+1\8+1\32-1\64=1\128得和.

用 错位相减法求：1\2-1\4+1\8+1\32-1\64=1\128得和.
用 错位相减法求：1\2-1\4+1\8+1\32-1\64=1\128得和.

用 错位相减法求：1\2-1\4+1\8+1\32-1\64=1\128得和.
另sn=1/2-1/4+1/8-1/16+1/32-1/64+1/128
1/2sn=1/4-1/8+1/16-1/32+1/64-1/128+1/256
3/2sn=1/2+1/256=129/256
sn=43/128

1/2-1/4+1/8+1/32-1/64
=1/4+1/4-1/4+1/8+1/32-1/64
=1/4+1/8+1/32-1/64
=2/8+1/8+1/64+1/64-1/64
=3/8+1/64
=24/64+1/64
=25/64≠1/128
你的题目有没有问题。其实是 1\2-1\4+1\8-1\16+1\32-1\64+...

全部展开

1/2-1/4+1/8+1/32-1/64
=1/4+1/4-1/4+1/8+1/32-1/64
=1/4+1/8+1/32-1/64
=2/8+1/8+1/64+1/64-1/64
=3/8+1/64
=24/64+1/64
=25/64≠1/128
你的题目有没有问题。

收起