e( 1/2x^2- 1)=2= 1/2e(x^2)- 1
So e (x 2) = 6.
According to the property of variance d (ax+b) = a 2d (x)
d( 1/2X- 1)= 1/2
So D(X)=2.
Because d (x) = e (x 2)-[e (x)] 2.
So e (x) = [e (x 2)-d (x)] (1/2) = 2.