有理数的乘法法则中包括“负负得正”一条,即“两个负有理数相乘,结果(积)是一个正有理数,其绝对值等于相乘两数的绝对值的乘积。”例如,(-2)×(-3)=+6。这条法则对刚学它的人来说,不是很容易理解,多数人是把它硬记下来的。记得水稻专家袁隆平院士说过他学正负数时想不清这个法则的道理,就去向老师 The law of multiplication for rational numbers includes a “negative and positive” one, that is, “multiply two negative rational numbers and the result (product) is a positive rational number whose absolute value is equal to the product of the absolute values ​​multiplied by two.” For example, -2) × (-3) = + 6. This rule is not very easy to understand for those who just learned it, and most people write it down. I remember the rice expert Yuan Longping academicians said he was learning positive and negative numbers can not figure out the truth of this law, went to the teacher