Question

数列2,2*1/2,3*1/4,4*1/8,...,n+1/2的n-1次方,求前n项和

Answer 1

1+1/1+2+1/2^1+.n+1/2^(n-1)

=n*(1+n)/2+1/2^0*(1-1/2^n)/1/2

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