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Name: Mehdi
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How do you explain -1*-1=+1 (without using velocity, direction and time)

Multiplication by -1 is reflection through the origin. A number becomes its counterpart on the other side of zero. Clearly, if you reflect a number twice through the origin (multiply twice by -1), then that is the same as doing nothing at all (multiplying once by 1).



My guess is that this is a concept, a convention, an assumption, or an agreement, based on which other relationships can be expressed and derived. I recommend looking into a reference book on the history of mathematics to learn about its invention and justifications.


Dr. Ali Khounsary

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