7
$\begingroup$

Possible Duplicate:
Why negative times negative = positive?

An Abstract Algebra text book has a sentence on its 1st chapter about natural numbers that i cannot get around easily. The sentence reads "Why minus multiplied by minus needs to be plus is something you might reflect on now." I cannot answer the question, why minus multiplied by minus needs to be plus? thanks

  • 0
    Which "Abstract Algebra" book? (It is not an idle question: I'm unsure at what level to answer this question... numbers, basic algebra, abelian groups...)2012-04-27
  • 0
    the book is: A first course in abtract algebra, rings, groups, and fields.2012-04-27

2 Answers 2