Multiplication of signed numbers might be performed through using the subsequent rules:
The product of any two numbers along with like signs is positive: (+)(+) = (+) or (-)(-) = (+).
The product of any two numbers along with unlike signs is negative: (+)(-) = (-) or (-)(+) = (-).
The product is negative if there are an odd number of negatives. The product is positive if there is an even number of negatives.
(+3)(+3) = +9 (-2) (+4) = -8
(-1) (-2) (+1) (-2) = -4 (-2) (+2) (+2) (-2) = +16
Zero times has any number equaled zero.
Multiplying through -1 is the equivalent of changing the sign.