4.4 Slope of a Line

Slope basically describes the steepness of a line

If a line goes up from left to right, then the slope has to be positive

Conversely, if a line goes down from left to right, then the slope has to be negative

Definitions of Slope

Slope is simply the change in the vertical distance over the change in the horizontal distance

12

12

xx

yy

run

risemslope

12

12

xx

yym

The formula above is the one which we will use to find the slope of specific lines

In order to use that formula we need to know, or be able to find 2 points on the line

12

12

xx

yym

Formula for SlopeA way to remember which value goes

on top.

2Y 1-Y2X 1- X

Keep the pairs together.

If a line is in the form Ax + By = C (what is this called??), we can use the following formula to find the slope:

B

Am

Examples

6,5,4,1 754 yx

)1(5

46

m

3

1

6

2m

5

4

m

5

4m

Horizontal lines have a slope of zero while vertical lines have no slope

HorizontalVertical

m = 0

m = no slope

horizontal line

y

What does an upside-down h look like?

= any number

Is always a horizontal line.

Vertical line

x

What does an upside-down and right-side up V look like?

= any number

Is always a vertical line.

Homework:

p. 239-240 #3-27 multiples of 3