D(X)=E(X^2) -[E(X)]^23 = E(X^2) -1E(X^2) = 4------------E[3（X^2-2）]=3E(X^2) - 6=12-6=6ans : B
D(X)=E(X^2)-[E(X)]^2E(X^2)=D(X)+[E(X)]^2=3+(-1)^2=4E[3(X^2-2)]=3E(X^2-2)=3E(X^2)-3E(2)=3*4-3*2=6
