Variance Definition(variance); The variance of a random variable X is VAr[X]=E[(X-E[X)2]=E[x2]-(EX])2 The standard deviation of random variable X is 6[X]=VVar[X]Variance Definition (variance): The variance of a random variable X is Var[X] = E ￾ (X ￾E[X])2⇥ = E ￾ X2⇥ ￾(E[X])2 . The standard deviation of random variable X is ￾[X] = ￾Var[X]