有些教师在指导学生判别正、反比例关系时说:“正比例关系式 y/x=k(一定)中的 k 不能为总量,而反比例关系式 xy=k(一定)中的 k 一定是总量。因此,k 为总量,则两量成反比例,否则两量便成正比例。”实际情况果真如此吗?当然,在一般情况下,这种说法好象没有错误,例如(总价/数量)=单价,(总数/份数)=每份数,单价×数量=总价,每份数×份数=总数等。但是,在某些特定条件下,情况并非如此。譬如 Some teachers, when instructing students to discriminate between positive and negative relations, said: “The positive proportional relation y / x = k (a) in the k can not be the total, and inverse proportion relation xy = k (a) k must be the total Therefore, if k is the total quantity, then the two quantities are in inverse proportion, otherwise the two quantities will be in direct proportion. ”Is this really the case? Of course, there are no mistakes in the general case such as (total price / quantity) = Unit price, (total number of copies) = number of copies, unit price × number = total price, number of copies × number of copies = total number, and the like. However, this is not the case under certain conditions. for example