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a(n+1)=2an +2^(n+1)
a(n+1)/2^(n+1) - an/2^n = 1
=> {an/2^n} 是等差数列, d=1
an/2^n - a1/2 = n-1
an/2^n = n
an= n.2^n
(3)
cn
=(n+2).2^n/{ an.a(n+1) }
=(n+2).2^n/[ n.2^n . (n+1).2^(n+1) ]
=(n+2)/[ n(n+1).2^(n+1) ]
=1/(n2^n) - 1/[ (n+1).2^(n+1) ]
Tn
=c1+c2+...+cn
=1/2 - 1/[ (n+1).2^(n+1) ]
a(n+1)/2^(n+1) - an/2^n = 1
=> {an/2^n} 是等差数列, d=1
an/2^n - a1/2 = n-1
an/2^n = n
an= n.2^n
(3)
cn
=(n+2).2^n/{ an.a(n+1) }
=(n+2).2^n/[ n.2^n . (n+1).2^(n+1) ]
=(n+2)/[ n(n+1).2^(n+1) ]
=1/(n2^n) - 1/[ (n+1).2^(n+1) ]
Tn
=c1+c2+...+cn
=1/2 - 1/[ (n+1).2^(n+1) ]
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