This formula refers to rational number multiplication, which means that two numbers are multiplied, the same sign is positive, the different sign is negative, and any number is multiplied by 0 to get 0. In fact, this formula is adapted according to the law of multiplication, which is beneficial to memory and application.
Multiplication rule of rational numbers:
1, the same sign is positive, the different sign is negative, and the absolute value is multiplied.
Any number multiplied by zero will get zero.
3. Multiply several numbers that are not equal to zero. The sign of the product is determined by the number of negative factors. When there are odd negative factors, the product is negative, and when there are even negative factors, the product is positive.
When several numbers are multiplied, if one factor is zero, the product is zero.
5. Multiply several numbers that are not equal to zero, first determine the sign of the product, and then multiply it by the absolute value.
Above content reference: Baidu Encyclopedia-Multiplication