Remember that when we work with natural numbers we define the multiplication as an addition in which all the summands are equal.
Let's see how to extend this reasoning to the numbers with signs.
First let's see if the addends are negative numbers would be:
Notes that, in this case, the factors have different signs and the product is a negative sign.
Based on the above two examples we can say that:
- If the factors are positive, the product is positive.
- If the factors have different signs the product is negative.
But what happens if both factors are negative?
need to investigate the abduction. Notes. If we subtract
(-3) five times, we can write as follows:
To calculate the product do all of these subtractions. To simplify the calculation we will add a leading zero. Remember that zero is the neutral of the sum does not affect the result.
The product of two negative numbers is a positive number!
We can summarize the cases studied in the following diagram:
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