证由于 E X k E(X)==nH={, k=1 =1 P\nk X 2 D(XN) n 由契比雪夫不等式可得 P Xk-1<E}≥1 =1 36 证 由于 , 1 ( ) 1 1 , 1 ( ) 1 1 2 2 2 1 2 1 1 1 n n n D X n X n D n n E X n X n E n k k n k k n k k n k k s s m m = =  =       = =  =           = = = = 2 2 1 / 1 1  s m  n X n P n k k  −        −  = 由契比雪夫不等式可得