Page 292 - Algebra 1

Example
4
Determining Slopes of Horizontal and Vertical Lines
Determine the slope of the given line.
a.
SOLUTION
_y 2 - y 1 m=_ x2 - x1
4-4 = 6 - (-6)
= _0 12
= 0
The slope is 0, or no slope.
b.
4
8
-4
-8
y
slope formula
Substitute the x- and y-values.
Simplify.
Math Reasoning
Generalize What is true about the x-coordinates of any line with an undefined slope?
2
O
(7, 1)
x
-2
-4
2
4
6
(7, -5)
SOLU_TION y2 - y1
m=_ x2 - x1
slope formula
Substitute the x- and y-values.
Simplify.
(-6, 4)
= (-5) -1 7-7
= -6 _
8
y
(6,
4)
x
-8
-4
0
The slope is undefined.
The slope of a vertical line is undefined because it has a zero in the denominator. The slope of a horizontal line has a zero in the numerator, therefore its slope is zero.
Lesson 44 277