College Algebra, 2013a

2.4 Inequalities with Absolute Value and Quadratic Functions 209
point on the graph of y = g(x) is(x, g(x)). When we seek solutions to f(x) =g(x), we are
looking for x values whose y values on the graphs of f and g are the same. In part 1, we
found x = 3 is the solution to f(x) =g(x). Sure enough, f(3) = 5 and g(3) = 5 so that the
point (3, 5) is on both graphs. In other words, the graphs of f and g intersect at (3, 5). In
part 2, we set f(x) 3, note that
the graph of f is above the graph of g, sincethey values on the graph of f are greater than
the y values on the graph of g for those values of x.
y
y
8
7
8
7
y = f(x)
6
5
4
y = g(x)
6
5
4
y = g(x)
3
3
2
1
y = f(x)
2
1
−1
1 2 3 4
x
−1
1 2 3 4
x
f(x) g(x) on(3, ∞)
The preceding example demonstrates the following, which is a consequence of the Fundamental
Graphing Principle for Functions.
Graphical Interpretation of Equations and Inequalities
Suppose f and g are functions.
ˆ The solutions to f(x) =g(x) arethex values where the graphs of y = f(x) andy = g(x)
intersect.
ˆ The solution to f(x) g(x) is the set of x values where the graph of y = f(x) above the
graph of y = g(x).
The next example turns the tables and furnishes the graphs of two functions and asks for solutions
to equations and inequalities.