(2)极点 若(=)=∑C(=-b),0<2-b<R m21Cm≠0有限项负幂 则二=b→()的m阶极点阶极点又称为单极点。 e.g.( ∑:2,0<2 z=0→二阶极点 而f(z) z2(=-1)2-1(2-1)+³ 1, ¹ 0(有限项负幂 ) m C- m f ( )z C (z b ) ,0 z b R, k k = å k - < - < ¥ = -¥ 若 则z=b→f(z)的m阶极点,1阶极点又称为单极点。 ( ) ( ) ,0 1 1 1 1 1 1 1 . . 0 2 2 2 < < - = - - = × - = å ¥ = z z z z z z z e g f z k k ∴z=0→二阶极点 1 ( ) ( ) ( ) = - + × - = - = 1 1 1 1 1 1 1 2 z z z z 而 f z (2).极点