离差平方和 简便公式推导 求助

Question

如题所述

Answer 1

∑（x-x拔）^2=∑(x^2-2xx拔+x拔^2)=∑x^2-2∑xx拔+∑x拔^2=∑x^2-2x拔nx拔+nx拔^2=∑x^2-nx拔^2=∑x^2-∑x^2/n