S^2=1/n[(x1-x)^2+(x2-x)^2……+(xn-x)^2] x為平均數(shù)
=1/n[x1^2……+xn^2-2(x1+x2……+xn)x+nx^2]
=1/n[x1^2……+xn^2-2nx*x+nx^2]
=1/n*(x1^2……+xn^2-nx^2)
所以對比可得到：n=10 nx^2=160
x=4或-4
平均數(shù)是4或-4