概车纶与款程统外「 又B=2(x-X2=2(x2-2x,X+) =12x2-X2=4-3, n i=1 (A,是样本二阶原点矩) 由大数定律知， 4=之x依概率收敛于E(X n -1 X=1∑X,依概率收敛于E(X), n i=1 = = − n i Xi X n B 1 2 2 ( ) 1 又 = = − + n i Xi XiX X n 1 2 2 ( 2 ) 1 = = − n i Xi X n 1 1 2 2 , 2 = A2 − X ( ) A2是样本二阶原点矩 由大数定律知, ( ), 1 2 1 2 2 X E X n A n i  i 依概率收敛于 = = ( ), 1 1 X E X n X n i  i 依概率收敛于 = =