20 13 The secondary root problem of mathematics in the classified training of senior high school entrance examination 26 - Training Enrollment Network

20 13 The secondary root problem of mathematics in the classified training of senior high school entrance examination 26

Solution: √ Sn = √ [1+2/n (n+1)+1/n 2 (n+! )^2]=√[ 1+ 1/n(n+ 1)]^2= 1+ 1/n(n+ 1)= 1+ 1/n- 1/(n+ 1)

Therefore, s =1+1-1/2+1/2+1/3+...+1+/n-65438.

=n+ 1- 1/(n+ 1)

=n(n+2)/(n+ 1)

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