College Algebra 9th txtbk

SECTION 1–3 Absolute Value in Equations and Inequalities 65
1-3 Absolute Value in Equations and Inequalities
Z Relating Absolute Value and Distance
Z Solving Absolute Value Equations and Inequalities
Z Using Absolute Value to Solve Radical Inequalities
We can express the distance between two points on a number line using the concept of
absolute value. As a result, absolute values often appear in equations and inequalities that
are associated with distance. In this section, we define absolute value and we show how to
solve equations and inequalities that involve absolute value.
Z Relating Absolute Value and Distance
We start with a geometric definition of absolute value. If a is the coordinate of a point on
a real number line, then the distance from the origin to a is represented by |a| and is referred
to as the absolute value of a. So |5| 5, since the point with coordinate 5 is five units
from the origin, and 6 6, since the point with coordinate 6 is six units from the
origin (Fig. 1).
6 6 5 5
6 0
5
x
Z Figure 1 Absolute value.
We can use symbols to write a formal definition of absolute value:
Z DEFINITION 1 Absolute Value
x if x 6 0
x
x if x 0
[Note: x is positive if x is negative.]
For example, 3 (3) 3
For example, 4 4
Both the geometric and algebraic definitions of absolute value are useful, as will be
seen in the material that follows. Remember:
The absolute value of a number is never negative.
EXAMPLE 1 Finding Absolute Value
Write without the absolute value sign:
(A) 3 (B) 3