2.单位冲激函数δ() p() 1/△ P()=,[E(t+-)-E(t- △→>0 → △/2|△/2t lim p(t=s(t) △→>0 定义 0(t≤0.) 8() 0(t≥0) s(tdt=1→    → 1 0 lim ( ) ( ) 0 p t =  t → 2. 单位冲激函数  (t)  / 2 1/  t p(t) - / 2 )] 2 ) ( 2 [ ( 1 ( )  − −  +  p t =  t  t 定义      = + 0 ( 0 ) 0 ( 0 ) ( ) - t t  t   −  (t)dt = 1 t (t) (1) 0