3方差的专业定义是随机变量的二次中心矩，与期望值之差的平方的加权平均值。
The technical definition of variance is the random variable's second central moment, the weighted average of the square of the differences from the expected value.
3方差的专业定义是随机变量的二次中心矩，与期望值之差的平方的加权平均值。
The technical definition of variance is the random variable's second central moment, the weighted average of the square of the differences from the expected value.
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