由题意可知:D(X)=E(X^2)-(E(X))^2=2
(X1-3)^2+(X2-3)^2+(X3-3)^2+……+(x10-3)^2=120,则E{(X-3)^2}=120/10=12
E(X^2)=E[{(X-3)+3}^2]=E[(X-3)^2+6(X-3)+9]=E[(X-3)^2]+6E[(X-3)]+9=12+6E[X]-6*3+9=3+6E[X]
即D(X)=E(X^2)-(E(X))^2=3+6E(X)-{E(X)}^2=2
E(X)=3+√10或E(X)=3-√10
由题意可知:D(X)=E(X^2)-(E(X))^2=2
(X1-3)^2+(X2-3)^2+(X3-3)^2+……+(x10-3)^2=120,则E{(X-3)^2}=120/10=12
E(X^2)=E[{(X-3)+3}^2]=E[(X-3)^2+6(X-3)+9]=E[(X-3)^2]+6E[(X-3)]+9=12+6E[X]-6*3+9=3+6E[X]
即D(X)=E(X^2)-(E(X))^2=3+6E(X)-{E(X)}^2=2
E(X)=3+√10或E(X)=3-√10