Math 7 (Period 4)

Using a Number Line to Add Integers 3.2

Adding integers on a Number Line-

To find the sum of two integers a and b

1)  Start at ZERO… and move  │a│ units to the right if a is positive or toe the left if a is negative

2) then move  │b│ units to the right, if b is positive or to the left it b is negative. The sum is the  final position on the number line.

Now it becomes easier to see some of the Rules of Integers…

To find the sum of two negative integers, first add the absolute values of the integers . Then use a negative sign to show that the sum of the integers is negative.

What do we do if the integers are both positive? That’s easy—you do what you have done since… 2^nd grade…

So, can we write a general rule?

Yes,  

The rule for adding integers with the same sign—just add the integers and use their sign!

What happens, however, if we are adding integers with Different signs?

We drew a number line to represent -7 + 3 and found it was equal to -4

We noticed that the absolute value of the sum of the integers │-4│  is the difference between the length of the longer arrow and the length of the shorter arrow.  The sign of the SUM (negative) is the same as the sign of the integer with the longer arrow on our graph…

To find the sum of two integers with different signs, find the absolute value of the integers. Then take the difference between the two absolute values. Use the sign of the integer with the larger absolute value.

The sum of 0 and any integer is that integer.