1、
略
2、
a(n+1)=4n+1
bn=1/4*4/(4n-3)(4n+1)
=1/4*[(4n+1)-(4n-3)]/[(4n-3)(4n+1)]
=1/4*{(4n+1)/[(4n-3)(4n+1)]-(4n-3)/[(4n-3)(4n+1)]}
=1/4*[1/(4n-3)-1/(4n+1)]
所以Sn=1/4*[1/1-1/5+1/5-1/9+1/9-1/13+……+1/(4n-3)-1/(4n+1)]
==1/4*[1-1/(4n+1)]
=n/(4n+1)
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