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2018-05-14
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(1)an=Sn-S(n-1)=2n²+2n-2(n-1)²-2(n-1)=4n,
bn/(4^n+1)=an-a(n-1)=4n-4(n-1)=4,
bn=4(4^n+1),
(2)cn=anbn/16-n=4n[4(4^n+1)]/16-n=n×4^n,
Tn=c1+c2+c3+...+cn=1×4^1+2×4^2+3×4^3+...+n×4^n,
4Tn=1×4^2+2×4^3+3×4^4+...+(n-1)×4^n+n×4^(n+1),
4Tn-Tn=n×4^(n+1)-(4^1+4^2+4^3+...+4^n),
3Tn=n×4^n+n-4(4^n-1)/3,
Tn=(n/3-4/9)×4^n+n/3+4/9
bn/(4^n+1)=an-a(n-1)=4n-4(n-1)=4,
bn=4(4^n+1),
(2)cn=anbn/16-n=4n[4(4^n+1)]/16-n=n×4^n,
Tn=c1+c2+c3+...+cn=1×4^1+2×4^2+3×4^3+...+n×4^n,
4Tn=1×4^2+2×4^3+3×4^4+...+(n-1)×4^n+n×4^(n+1),
4Tn-Tn=n×4^(n+1)-(4^1+4^2+4^3+...+4^n),
3Tn=n×4^n+n-4(4^n-1)/3,
Tn=(n/3-4/9)×4^n+n/3+4/9
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