7-10 事实上,按矩法原理,令 X=∑X= 71 A=∑X=E(X2) l= X E(X -E(X=A, r2X-X=2(cX-1)=s7 -10 事实上，按矩法原理，令 =  =  =ni Xi n X 1 1 ( ) 1 2 1 2 2 X E X n A n i =  i = = ˆ = X   ˆ = ( )− ( ) 2 2 2  E X E X 2 2 = A − ˆ 2 2 1 1 n i i X X n = = −  2 1 2 ( ) 1 n n i i X X S n =  − = =