It is known that the variance of a set of data x1, X2, X10 is 2, and (x1)

It is known that the variance of a set of data x1, X2, X10 is 2, and (x1)

Original question: given a group of data x1, X2, X10 variance is 2, and (x1-3) ^ 2 + (x2-3) ^ 2 +... + (x3-3) ^ 2 +... + (x10-3) ^ 2 = 120, find the average X. given a group of data x1, X2, X3., X10 variance is 2, so (x1-x) ^ 2 + (x2-x) ^ 2 +... + (x10-x) ^ 2 = 20 (x1-3) ^ 2 + (x2-3) ^ 2

It is known that the variance of a set of data x1, X2,... X10 is 2
It is known that the variance of a group of data x1, X2,... X10 is 2, and (x1-3) ^ 2 + (x2-3) ^ 2 +... + (x10-3) ^ 2 = 120, find the average of this group of data

Let Y1 = x1-3, y2 = x2-3, Y3 = x3-3 , Y10 = x10-3, the sequence variance is 2, then the sequence Y1 ^ 2, Y2 ^ 2, Y3 ^ 2 The variance of Y10 ^ 2 is 4 (x1-3) ^ 2 + (x2-3) ^ 2 +... + (x10-3) ^ 2 = Y1 ^ 2 + Y2 ^ 2 + Y3 ^ 2 + +Y10 ^ 2 = 120 because the sequence Y1 ^ 2, Y2 ^ 2, Y3 ^ 2 The variance of Y10 ^ 2 is 4, so Y5

Given a set of data, x1, X2, X3 The variance of x 10. Is 2
And the square of (x1-3) + (x2-3) + The square of + (10-3) is equal to 120

Minus one by half plus minus half by one-third plus minus one-third by one-quarter Plus minus one in 2009 multiplied by one in 2010
How much is it,

-（1/1）*（1/2）-（1/2）*（1/3）-…… -（1/2009)*(1/2010)=(-1/1+1/2)+(-1/2+1/3)+(-1/3+1/4)+…… +(-1/2009+1/2010)=-1/1+1/2-1/2+1/3-1/3+1/4+…… -1/2009+1/2010=-1+1/2010=-2009/2010

Minus one times one half equals minus one plus one half. Why? It's due tomorrow!

(- 1) × 1 / 2 = - 1 × 1 / 2 = - 1 / 2 according to the rule of rational number multiplication, the same sign gets the positive sign, the different sign gets the negative sign, and then the absolute value is multiplied
(- 1) + 1 / 2 = - (1-1 / 2) = - 1 / 2 is the sign of adding two numbers with different sign according to the rule of rational number addition to take the addend with larger absolute value, and subtracting the number with smaller absolute value from the number with larger absolute value

Minus one times one half = minus one plus one half; minus one half times one third = minus one half plus one third; minus one third times one fourth
What's the law of life

-1*1/2=-1+1/2
-1/2*1/3=-1/2+1/3
-1/3*1/4=-1/3+1/4
.
-1/n*1/(n+1)=-1/n+1/(n+1)