Multiplication of signed numbers
Use the following rules for multiplying integers.
|Multipliying Integers with the Same Signs
||The product of two integers with the same sign is positive.
|Multiplying Integers with Different Signs
||The product of two integers with different signs is negative.
Find the products:
The two integers have different signs.
Their product is negative.
16 · (-2) = -32
The two integers have the same sign.
Their product is positive.
(-30) · (-5) = 150
Rules of signs
( + ) x ( + ) = ( + )
( + ) x ( - ) = ( - )
( - ) x ( - ) = ( + ) ( - ) x ( + ) = ( - )
In finding the product of more than two numbers, you must remember that we operate on only two numbers at a time. So we start by finding the product of any two and continue until we have used all the factors.
An easy way to find the sign of the product is to count the number of minus signs. An even number of minus signs will produce a positive product.
The multiplication sign can be omited: (+3)x(-7) = (+3)(-7) = (-21)