确定收敛环 ∑2K( ∑2K(-1)+∑ k k: 一0 k=1 ∑ 1)+∑2-(二-1) k=0 正幂部分 ∑2(=-1 =m-1 lim(2)K=lim 2 k→>∞ (2 k/kk→>o 负幂部分 R2=1/im-_yk1/∞o=0 k→>∞(2确定收敛环 2 2 ( 1) k k k z  − =−  − 2 2 0 1 2 ( 1) 2 ( 1) k k k k k k z z  − − =− = = − + −   2 2 0 1 2 ( 1) 2 ( 1) k k k k k k z z   − − − = = = − + −   正幂部分 2 1 2 ( 1) k k k z  − =  − 2 2 1/ 1 1/ 1 lim lim(2 ) lim 2 (2 ) k k k k k k k k R → → → − = = = =  负幂部分 2 2 1/ 1 1/ lim 1/ 0 (2 ) k k k R → − = =  =