查看原题'" class='mdui-btn mdui-btn-raised'>点击加载点击跳转$$\frac{1}{n}\sum_{i=1}^{n}(a_i-\bar a)^2\\= \frac 1n \sum_{i=1}^{n}(a_i^2-2\bar a\times a_i+{\bar a}^2)\\= \frac 1n (\sum_{i=1}^nai^2 - 2\bar a\sum{i=1}^n a_i + n \bar a^2)\\= \frac 1n \sum_{i=1}^n a_i^2 - \bar a^2$$……