取k=10 丌≈41--+ =3.232316 35 1921 取k=20 丌≈41-+ 十 3.189184 35 3941取 k = 20 3.189184 4 11 3 91 51 31 4 1  =     − + −  − + 取 k = 10 3.232316 2 11 1 91 51 31 4 1  =     − + −  − +