For any real numbers a and b If a lt; b then -a gt; -b If a gt; b then -a lt; -b
If a is the multiplicative inverse of b, then: ab 1 a 1 / b and b 1 / a. Similarly if a is the additive inverse of b, then: a + b 0 a -b and b -a. The additive inverse is therefore the same as multiplying by -1, as you say. It doesn't explain the reversal of the signs, though, when you take additive inverses.
Yes, it can be dangerous if it is eaten by infants.
