I can't figure out why the statement below is true. I am also confused why the first statement uses square brackets but the second statement uses round brackets. Please advise.
The variance of a random variable tells us something about the spread of the possible values of the variable. For a discrete random variable X, the variance of X is written as Var(X).
$Var(X) = E[(X - m)^2]$ where m is the expected value E(X)
This can also be written as:
$Var(X) = E(X^2) - m^2$