Question

the variance of X is​

Answer 1

Answer:

So the variance of X is the weighted average of the squared deviations from the mean μ, where the weights are given by the probability function pX(x) of X. The standard deviation of X is defined to be the square root of the variance of X. That is, sd(X)=σX=√var(X).

Answer 2

Answer:

Var[X+Y] = Var[X] + Var[Y] + 2∙Cov[X,Y] . Note that the covariance of a random variable with itself is just the variance of that random variable. While variance is usually easier to work with when doing computations, it is somewhat difficult to interpret because it is expressed in squared units.