由an+2-3an+1+2an=0,得an+2-an+1=2(an+1-an)所以{an+1－an}是等比数列,即an+1－an=(a2－a1)•2n-1=3•2n-1再注意到a2－a1=3,a3－a2=3•21,a4－a3=3•22,…,an－an-1=3•2n-2,这些等式相加,...