Page 273 - Algebra 1

A line with a positive slope rises from left to right. A line with a negative slope falls from left to right. There are two other cases to consider: horizontal and vertical lines.
Horizontal and Vertical Lines
The graph of the equation y = c, where c is a constant, is a horizontal line. The slope of a horizontal line is 0.
The graph of the equation x = c, where c is a constant, is a vertical line. The slope of a vertical line is undefined.
vertical
h
orizonta
l
4
O
y
x
-4
-2
-2
2
4
-4
O
Graphing Horizontal and Vertical Lines
Example
4
a. Find the slope of the horizontal line.
b. Find the slope of the vertical line.
y
8
8
(6,
4)
4
(2, 8)
(2, 4)
x
O
(2, 4)
x
-8
-4
4
8
-8
-4
8
-4
-8
SOLUTION Find the ratio of the rise to the run.
SOLUTION Find the ratio of the rise to the run.
__ __
slope= rise = 4-4 run 6-2
slope= rise = 8-4 run 2-2
= _4
The slope is 0 because 0 divided by The slope is undefined because any
any nonzero number is 0. number divided by 0 is undefined.
Application: Cooking
The graph and table show the relationship between the number of servings a salsa recipe makes and the ounces of black beans used to make this recipe.
= _0 40
-8
4
-4
Example
5
Servings
4
6
10
18
Black Beans (oz)
10
15
25
45
(18, 45)
258 Saxon Algebra 1
a. Use the table or graph to find the slope of the line.
45 35 25 15
y
(6, 15)
5
Number of Servings
2 6
10 14 18
Black Beans (oz)