而 P(A+2E)P =P-AP+P-(2E)P 2+2 =Λ+2E= 九2+2 故A+2E=P(A+2E)P =(2+2(22+2)(2n+2) 因为2>0，(i=1,2,…,n) A+2E>2”               + + + =  + = = + + − − − 2 2 2 2 (2 ) ( 2 ) 2 1 1 1 1 n E P AP P E P P A E P     而 2 2 . 0,( 1,2, , ) ( 2)( 2) ( 2) 2 ( 2 ) 1 2 1 n i n A E i n A E P A E P +   = = + + + + = + −       因为 故