why does the variance of $x-y$ equal to the sum of the variances when the variances for $x,y$ are independent and not normally distributed? what is the sum variance of x and y in math? when xy is independent, why is variance equal to the sum of the variances why is variance equal to the sum of the variances when $x,y$ are independent why is the variance of $x-y$ equal to the sum of the variances when $x,y$ are independent and normally distributed random variables? why is the variance of $x-y$ equal to the sum of the variances when $x,y$ are independent? why is variance equal to the sum of variances when why is variance equal to the sum of variances when why is the variance of _____ x-y equal to the sum of the variances when _____ and _____ are independent and normally distributed random variables? why is variance equal to sum of variances why is the variance of $x-y$ equal to the sum of the variances when $x,y$ are independent? why is variance equal to variance of $x-y$ what is the variance of an independent variable called why is the variance of x-y=as a function of the sum of the variances when x-y=as independent and normally distributed why is variance equal to the sum of variances when xy$ is independent what is variance if y is independent, how is variance calculated? what is the variance of $x-y$ when $x is independent what is the variance of xy when $qy is independent? why is the mean of variance of $X-Y