已知数列{log2 (an-1)}为等差数列,且a1=3 a3=9 (1)求an (2)证明1/（a2-a1)+1/(a3

题目

已知数列{log2 (an-1)}为等差数列,且a1=3 a3=9 (1)求an (2)证明1/（a2-a1)+1/(a3
an已经求出,an=2^n +1
(2)证明1/（a2-a1)+1/(a3-a2)+…+1/a(n+1)-an

答案