a1=1,a(n+1)=Sn+3n+1,bn=(2的n次方)/an*a(n+1)

1个回答

  • 【解】:

    S[n]=a[n+1]-3n-1;S[n-1]=a[n]-3(n-1)-1=a[n]-3n+2

    a[n]=S[n]-S[n-1]=(a[n+1]-3n-1)-(a[n]-3n+2)=a[n+1]-a[n]-3

    得:a[n+1]=2a[n]+3

    即:(a[n+1]+3)=2×(a[n]+3)

    所以{a[n]+3}为以2为公比的等比数列,且a[1]+3=4;

    则:a[n]+3=4*2^(n-1)=2^(n+1)

    得:a[n]=2^(n+1)-3

    得:b[n]=2^n/(2^(n+1)-3)(2^(n+2)-3)=2/(2^(n+1)-3)-1/(2^(n+2)-3)

    b[1]=2/(2^2-3)-2/(2^3-3)

    b[2]=2/(2^3-3)-2/(2^4-3)

    b[3]=2/(2^4-3)-2/(2^5-3)

    ……

    b[n-1]=2/(2^n-3)-2/(2^(n+1)-3)

    b[n]=2/(2^(n+1)-3)-2/(2^(n+2)-3)

    相加消项得:T[n]=2/(2^2-3)-2/(2^(n+2)-3)=2-2/(2^(n+2)-3)

    |(T[n]-1)/2|1/2010.

    显然题目这个有点问题,不知何意.