矩，动差任意变量的正整数功效的期望值、。第一个矩是分配的平均数 The expected value of a positive integral power of a random variable. The first moment is the mean of the distribution.
人们使用轧机把材料加工成各种形状┃，如圆棒材┃、方棒材和矩形棒材。 A rolling mill is used to form the material into various form such as round rod, square or rectangular bar.
