S=1/2+1/4+1/8+...1/256
1/2*S=1/4+1/8+1/16+...+1/256+1/512
两个式子相减,得
1/2*S=1/2-1/512
1/2+1/4+1/8+1/16+1/32+...+1/256
=255/256
解答:
1/2+1/4+1/8+1/16+1/32+...+1/256
=1/2+1/4+1/8+1/16+1/32+...+1/256+1/256-1/256
=1/2+1/4+1/8+1/16+1/32+...+1/128+1/128-1/256
=1/2+1/4+1/8+1/16+1/32+1/64+1/64-1/256
=1/2+1/4+1/8+1/16+1/32+1/32-1/256
=……
=1-1/256=255/256