MINUS (NEGATIVE) SIGNS
The seemingly benign set of rules for manipulating a minus sign nevertheless manages to cause an endless set of headaches. Let’s see if I can summarize these rules quickly and clearly:
1. (Not so much a rule as a reminder) When a sign is not shown, a positive sign is implied:
34 = +34,
(35) = (+35) =+(35).
2. Subtracting B from A is the same as adding – B to A:
7 – 5 = 7 + (-5) = 2.
3. As implied above, multiplying a positive number by a negative number yields a negative number:
(-3)(6) = -(3)(6) = -18,
(-6 ) = -(6 ) = (-1)(6).
4. Multiplying two negative numbers yields a positive number:
(-5)(-7) = +35.
Division rules are the same as multiplication rules. Dividing a positive number by a negative number or dividing a negative number by a positive number yields a negative number. Dividing a negative number by a negative number yields a positive number: