1. Ch 4.1 (part 2) Slope (formula)
Objective:
To find the slope of a line when given two points.

2. Distribute the negative: change the signs for x1 and y1
Definition
Slope (m): formula
m = y2 – y1
x2 – x1
where (x1, y1) is a point and (x2, y2) is another point.
It is important to keep the coordinates “in line” otherwise the sign will be reversed.
Use when given 2 points
EASY way to find the slope
(x2, y2) − −
( x1, y1) - -
Distribute the negative: change the signs for x1 and y1
y2 – y1
x2 – x1

3. Example 1 Example 2 (-1, 3) (6, 5) ( 4, 7) (-1, 7) m = m =
Find the slope between (-1, 3) and (4, 7).
Find the slope between (6, 5) and (-1, 7).
(-1, 3)
(6, 5) − − −
( 4, 7) - - −
(-1, 7) - −
3 - 7
5 - 7 -4 -2 = =
-1 - 4
6 + 1 -5 7 4 -2
m =
m = 5 7

4. Example 3 Example 4 (-8, 7) (1, 2) ( 4, 1) (-2,-3) m = m =
Find the slope between (-8, 7) and (4, 1).
Find the slope between (1, 2) and (-2,-3).
(-8, 7)
(1, 2) − − −
( 4, 1) - - −
(-2,-3) − −
7 - 1
2 + 3 6 5 = =
-8 - 4
1 + 2
-12 3 -1 5
m =
m = 2 3

5. Example 5 Example 6 (-3, 2) (-1, 4) ( 4, 2) (-1,-5) m = m =
Find the slope between (-3, 2) and (4, 2).
Find the slope between (-1, 4) and (-1,-5).
(-3, 2)
(-1, 4) − − −
( 4, 2) - - −
(-1,-5) − −
2 - 2
4 + 5 9 = =
-3 - 4
-1 + 1 -7
m =
m =
undefined

6. Find the slope between the following points.
Classwork
Find the slope between the following points. 1)
(1, 2) & (3, 4) 2)
(-3, 4) & (1, 2) 3)
(2, 5) & (4, 8) 4)
(4, 5) & (1, 5)

7. 5)
(7, 3) & (5, 4) 6)
(3, 6) & (5, 3) 7)
(6, 2) & (6, 7) 8)
(10, 5) & (5, 5)