Positive and Negative Integers
Positive integers are all the natural numbers greater than zero:
1, 2, 3, 4, 5, ...
Negative integers are all the opposites of these natural numbers:
1, 2, 3, 4, 5, …
We do not consider zero to be a positive or negative number. So, the opposite of 0 is 0. For each positive integer, there is a negative integer, and these integers are called opposites.
For example, 3 is the opposite of 3, 21 is the opposite of 21, and 8 is the opposite of 8.
If an integer is greater than zero, we say that its sign is positive.
If an integer is less than zero, we say that its sign is negative.
Absolute Value
 a + b  < c means – c < a + b < c
Problem: x + 3 < 7
Use the formula to solve:
7 < x + 3 < 7
Subtract 3 from each section:
7 < x + 3 < 7
3 3 3
10 < x < 4
OO
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109 8 7 6 5 4 3 2 1 0 1 2 3 4
