题目来源于知乎同名问题https://www.zhihu.com/question/20099757
主要参考了各答主了的答案
公式markdown还不会用，直接传图了，源文件在图下面
源文件：
https://github.com/MaHaLo-G/Storage_Public/blob/master/sample%20variance%20explore.docx
参考目录：
https://www.zhihu.com/question/52367271
https://www.zhihu.com/question/20099757
https://en.wikipedia.org/wiki/Bias_of_an_estimator#Sample_variance
https://math.stackexchange.com/questions/1363505/prove-that-e-overlinex-mu2-frac1n-sigma2
