1
MA 15200
Lesson 22
Sections 2.3 and 2.4
I
Slope of a Line
A measure of the ‘steepness’ of a line is called the
slope
of the line.
Slope compares a
vertical change (called the
rise
) to the horizontal change (called the
run
) when moving
from one point to another point along a line.
Slope is a ratio of vertical change to horizontal change.
If a nonvertical line contains points
)
,
(
and
)
,
(
2
2
1
1
y
x
y
x
, the slope of
the line is the ratio described by
2
1
2
1
change in y
change in x
y
y
rise
m
run
x
x

=
=
=

.
*Note:
Always be consistent in the order of the coordinates.
There are 3 ways to find slope.
1.
Using the slope formula (above)
2.
Counting rise over run (when shown a graph)
3.
Finding the equation in slopeintercept form
(later in lesson)
If a line is horizontal, the numerator in the slope formula will be 0 (the y coordinates of
all points of a horizontal line are the same).
The slope of a horizontal line is 0.
If a line is vertical, the denominator in the slope formula will be 0 (the x coordinates of
all points of a vertical line are the same).
A number with a zero denominator is not
defined or undefined.
The slope of a vertical line is undefined.
There are 4 types of slopes
.
Positive
Negative
Zero
Undefined
When given two
points, it does not
matter which one is
called point 1 and
which point 2.
2
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 Fall '09
 Slope

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