棍丰伦与散理统针」 E(X)=x(+x)dx+fx-x)dx 6 于是 D(X)=E(X2)-E(X)  = + + − − 1 0 2 0 1 2 2 E(X ) x (1 x)d x x (1 x)d x , 6 1 = 于是 2 2 D(X) = E(X ) − [E(X)] 2 0 6 1 = − . 6 1 =