"Unbiased estimator is the estimator of for which (for every value of Thus is unbiased if its sampling distribution is always "centered" at the true value of the parameter..."

Question continues as follows:

Unbiased estimator O is the estimator of 0 for which E(0) = 0 for every value of 0. Thus O is unbiased if its sampling distribution is always "centered" at the true value of the parameter. For example, if 0 = 100 then O is centered at 100. 62 = $2 = E (X; - X) 2 Prove that n - 1 is unbiased estimator of o2. Where X1, X2, . . ., , is random sample from a distribution with mean u and o2