A=AV,-AX|XeP"lV,-(XXeP",AX=0西安毛子科技大枣三XIDIAN UNIVERSITY任取αnV，即αV且αV由αV，必有βP"，使Aβ=α.由αV,，有Aα=0.从而 α= Aβ=A'β= A(Aβ)= Aα=0... Vnv, =(0)所以 p" =V④V2. = V V 1 2 0 2 由   = V A , 0. 有 1 , . n 由      = V P A 必有 , 使 任取 1 2 1 2       V V V V , 即 且 . 2 从而      = = = = = A A A A A ( ) 0. 1 2 . n 所以 P V V =  2 A A =