HORIZONTAL AND VERTICAL LINES Recall from Chapter 4 that the
slope of a horizontal line is zero and the slope of a vertical line is undefined.
In Example 4 you will learn how to write equations of horizontal and vertical
lines in standard form.
Student Help
STUDY TIP
Notice that there is no
x-term in the standard
form of a horizontal
line and no y-term in
the standard form of a
vertical line.
Equations of Horizontal and Vertical Lines
4
EXAMPLE
Write an equation of the blue line in standard form.
a.
b.
y
y
3
1
3
1
1
1
3 x
1
3
1
1
1
3 x
Solution
a. Each point on this horizontal
b. Each point on this vertical line
line has a y-coordinate of 3. So,
the equation of the line is y 3.
has an x-coordinate of 2. So, the
equation of the line is x 2.
Both equations are in standard form.
Equations of Horizontal and Vertical Lines
Write an equation of the line in standard form.
6.
7.
y
y
3
3
1
3
1
3
3 x
1
1
1
3 x
LINEAR EQUATIONS You have now studied all of the commonly used forms of
linear equations. They are summarized in the following list.
SUMMARY
Equations of Lines
SLOPE-INTERCEPT FORM:
POINT-SLOPE FORM:
VERTICAL LINE
y mx b
y y1 m(x x1)
(Undefined Slope): x a
HORIZONTAL LINE
STANDARD FORM:
(Zero Slope): y b
Ax By C, where A and B are not both zero.
5.4
Standard Form
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