S = 1/4 +1/8+1/16+1/32+1/64 (1)(1/2)S = 1/8 +1/16+1/32+1/64+1/128 (2) (1)-(2)(1/2)S = 1/4 -1/128 = 31/128S = 31/64 1/4 +1/8+1/16+1/32+1/ = S =31/64
哦,说错了,先不回答