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:
a. 16·(-2)
The two integers have different signs.
Their product is negative.
16 · (-2) = -32 |
b. (-30)·(-5)
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.
(+2)x(-3)x(+4)=(-6)x(+4)=-24
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.
Note: The multiplication sign can be omited: (+3)x(-7) = (+3)(-7) = (-21)