The discussion revolves around calculating the variance of the function Y=3x^2+3x+3, focusing on the assumptions and interpretations involved in the variance calculation.
The discussion is ongoing, with participants exploring the implications of their assumptions. Some guidance has been offered regarding the need to consider covariance, but no consensus has been reached on the correct approach.
There is a noted assumption that covariance between X^2 and X is zero, which some participants challenge. The presence of a potential typo regarding variable notation (z vs. x) is also mentioned.
I guess the z should be X, or 9var(x) should be 9Var(Z). Either way, what assumption does that step require?hellokitten said:Var(3x^2 +3z +1) = 9Var(x^2) +9Var(x)
haruspex said:I guess the z should be X, or 9var(x) should be 9Var(Z). Either way, what assumption does that step require?
hellokitten said:Homework Statement
Find the variance of Y=3x^2+3x+3The Attempt at a Solution
Let Y = 3x^2 +3x +3
Var(Y) = Var(3x^2 +3x +3) = 9Var(x^2) +9Var(x) = 9 [E[X^4] - E[X^2]^2 +E[X^2] - E[X]^2]
This is wrong.