概车纶与款理统外 _元-3m2+24, 16 因为D(X)=E(X2)-E(X), 所以D(X2)=E(X4)-[E(X2)I2 6r*-任-列 =20-2π2.( ) ( ) [ ( )] , 2 2 因为 D X = E X − E X 2 2 2 4 2 4 3 24 16         −  −  + −  = 20 2 . 2 = −  3 24, 16 2 4 −  +  = 2 4 2 2 所以 D(X ) = E(X ) − [E(X )]