an = 1/[(2n-1)(2n+1)]= (1/2)[(2n-1) -1/(2n+1) ]Sn = a1+a2+...+an= (1/2)[1 -1/(2n+1) ]= n/(2n+1)1/(1x3)+1/(3x5)+...+1/(23x25)=S12=12/2525x[1/(1x3)+1/(3x5)+...+1/(23x25)]=25x12/25=12
