81级数的收敛性 从而S=习2(ak+1)-(+1k+2) (n+1)(n+2) 故该级数收敛,其和为 (4)因为其通项为 an=√n+2-2√n+1+√n=√n+2-√n+1 1 n+1+√n 所以 √k+2+√k+ n+2+√n+1 1 故该级数收敛且其和为1-2 (5)S-1 sn=(+3+…+2n1)-(1.(1)2 3…()3+5:()4+…+(2n-1)()n+ =1+2·(1)2+2·(1)3+…+2.(1) -(2n-1)·() +…+nn=2)]-(2n-1)()