1/2+1/4+1/8+1/16+...+1/二的n次方等于?

1/2+1/4+1/8+1/16+...+1/二的n次方等于?

[1/2-1/2^(n+1)]/(1-1/2)
=1-1/2^n

原式乘以2，再减去原式就出来了

(1/2*(1-(1/2)^n))/(1-1/2)
=1-(1/2)^n