Sagot :
Answer: Not closed under multiplication
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Explanation:
Pick any two negative numbers that you want.
I'll go for -3 and -5
They multiply to (-3)*(-5) = 15 which is a positive number. The two negatives cancel out to form a positive.
This is an example to show that multiplication is not closed for this subset of the real numbers. We consider it to be closed if the result of any two negative numbers multiplied would get us some other negative number.
In a sense, this is the complete opposite of closed since the result is never negative.
Here's an example of a set that is closed under multiplication: integers
Picking any two integers and multiplying them together gets us some other integer. Each item is found in the same set, i.e. the result never leaves or goes outside the set.