1. 4-1B The Slope Formula First a quick review of the types of slope!
Algebra Glencoe McGraw-Hill Linda Stamper

2. Types of Slope
Imagine that you are walking to the right on a line.
A positive slope means that you are walking uphill.

3. Types of Slope
Imagine that you are walking to the right on a line.
A negative slope means that you are walking downhill.

4. Types of Slope
Imagine that you are walking to the right on a line.
Zero slope means that you are walking on level ground.
Do not identify this as “no slope”.

5. Types of Slope
Undefined slope is a vertical line. You can not walk up a vertical line. It is not possible. You would fall!
ouch!
Do not identify this as “no slope”.

6. What do you already know about the sign of the answer?
In the previous lesson you determined slope by plotting the points on a coordinate plane and then calculating the ratio of rise to run.
Find the slope of the line. y • • x
What do you already know about the sign of the answer?
It does not matter at which point you begin the walk!

7. Today you will find slope using ordered pairs in the slope formula.
Let m = slope.

8. • • Find the slope of the line.y • • x
After labeling the points, you must subtract the coordinates in the same order in both the numerator and the denominator.

9. All your problems MUST start with the slope formula!
Find the slope of the line that passes through the points
Stack the points.
Write the formula.
Substitute.
All your problems MUST start with the slope formula!
Simplify.
Place the negative sign before the fraction.
Slope is a numerical value!
Stacking method from JoAnn Evans (Redwood).

10. Find the slope of the line that passes through the given points
Example 1
Example 2
Example 3
Example 4

11. Slope is a numerical value!
Example 1 Find the slope of the line that passes through the points
Stack the points.
Write the formula.
Substitute.
Simplify.
Slope is a numerical value!

12. Zero oooooover the fraction line is
Example 2 Find the slope of the line that passes through the points
Zero oooooover the fraction line is
zeroooooo.

13. Zero unnnnder the fraction line is unnnnndefined.
Example 3 Find the slope of the line that passes through the points
Zero unnnnder the fraction line is unnnnndefined.
Slope is a word!

14. Example 4 Find the slope of the line that passes through the points
Slope is a numerical value!
Place the negative sign before the fraction.

15. You are to find the x-coordinate. The graph will NOT be given!
Given the slope of a line and one point on the line, you can find other points on the line.
Find the value of r so that the line through (r,4) and
(-3,0) has a slope of • • x
You are to find the x-coordinate. The graph will NOT be given! y

16. Find the value of r so that the line through (r,4) and
(-3,0) has a slope of .
Stack the points.
Write the formula.
Substitute.
Undo double sign.
Use cross products to solve.
The slope is given!

17. Find the value of r so the line that passes through each pair of points has the given slope.
Example 5 (1,4) and (-1,r) has a slope of 2
Example 6 (r,2) and (6,3) has a slope of

18. Example 5 Find the value of r so that the line through (1,4) and (-1,r) has a slope of 2.

19. Example 6 Find the value of r so that the line through
(r,2) and (6,3) has a slope of

20. Practice Problems
Find the slope using the slope formula.
(4,5) and (2,2) ) (6,1) and (– 4,1)
(2,2) and (–1,4) ) (3,6) and (3,–1)
5. (2,-1) and (3,4) ) (-3,-7) and (3,-7)
undefined 5

21. Homework
4-A3 Page # 20-39,64-65,68-71.