还记得初中数学课程里有乘法结合律,抽出公因数放到括弧外头,例如 AB+AC 的 A 是公因数,于是把它抽出,写成 A(B+C)。在数学上,这是个用作化简算式的概念。当然,学生不单要知道 AB+AC 可写成 AB+C,也应懂得倒过去,把 AB+C展开成 B+AC。括弧内的 B 与 C 是两个独立的个体。其实它们是有关系的,关系来自算式内共同拥有 Remember the junior high school mathematics curriculum with multiplication law, the common factor out of the brackets, such as AB + AC A is the common factor, so take it out, written A (B + C). Mathematically, this is a concept used as a simplification. Of course, students should not only know that AB + AC can be written as AB + C, but also should know how to reverse AB + C into B + AC. B and C in parentheses are two independent individuals. In fact, they are related, the relationship between the common ownership within the formula