1+2的负1次方+2的负2次方+2的负3次方+...+2的负1000次方
=1+1/2+1/2^2+1/2^3+...+1/2^1000
=1+1/2+1/2^2+1/2^3+...+1/2^1000+1/2^1000-1/2^1000
=2-1/2^1000
1+2的负1次方+2的负2次方+2的负3次方+...+2的负1000次方
=1+1/2+1/2^2+1/2^3+...+1/2^1000
=1+1/2+1/2^2+1/2^3+...+1/2^1000+1/2^1000-1/2^1000
=2-1/2^1000