Question

已知函数y=3x-2^-x，当x依次取1,2,3,…,n时，所得的y值之和是(    )

A.n(2n+1)-                               B.

C.                            D.

Answer 1

B

解析：3(1+2+…+n)-(2^-1-1+2^-2+…+2^-n)=.