This is a formal justification, from the ring axioms, of the formula (−a)(−b) = ab. As the article mentions, this is often phrased as "the product of two negat

This is a formal justification, from the ring axioms, of the formula (−a)(−b) = ab. As the article mentions, this is often phrased as "the product of two negatives is positive," but, of course, the presence of a minus sign in front of a variable does not indicate a negative number (for example, if a = −3, then −a is positive); and the formula makes sense even in a ring with no notion of positive and negative numbers.