写错了是1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256+1/512令a=1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256+1/5122a=1+1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256相减中间相同的抵消2a-a=1-1/512所以1/2+1/4+1/8+1/16+1/32+1...