1, if the average value of x 1, x2, x3...xn is m, the variance formula can be expressed as: D(CX)=C2D(X) (variance is not negative).

2. Variance formula is a mathematical formula and an important formula in mathematical statistics. It is applied to all kinds of things in life. The smaller the variance, the more stable the data set, and the larger the variance, the more unstable the data set.

3. If X and Y are independent of each other, then the first two items are just D(X) and D(Y), and the third item is expanded. When x and y are independent of each other, the third term is zero.