College Algebra 9th txtbk

140 CHAPTER 2 GRAPHS
So the graph of y b is a horizontal line crossing the y axis at (0, b). We summarize these
results as follows:
Z THEOREM 4 Vertical and Horizontal Lines
Equation
Graph
x a (short for x 0y a) Vertical line through (a, 0)
(Slope is undefined.)
y b (short for 0x y b) Horizontal line through (0, b)
(Slope is 0.)
y
x a
b
y b
a
x
EXAMPLE 6 Graphing Horizontal and Vertical Lines
Graph the line x 2 and the line y 3.
SOLUTION
y
5
y 3
5
x 2
5
x
5
MATCHED PROBLEM 6
Graph the line x 4 and the line
y 2.
The various forms of the equation of a line that we have discussed are summarized in Table 2
for convenient reference.
Table 2 Equations of a Line
Standard form Ax By C A and B not both 0
Slope–intercept form y mx b Slope: m; y intercept: b
Point–slope form y y 1 m(x x 1 ) Slope: m; Point: (x 1 , y 1 )
Horizontal line y b Slope: 0
Vertical line x a Slope: Undefined