1. Slope and Rate of Change Equations of Lines
Section 3.4 & 3.5
Slope and Rate of Change
Equations of Lines

2. Slope and Rate of Change
Find the slope of a line given two points on the line.
Find the slope of a line given its equation.
Find the slopes of vertical and horizontal lines.
Compare the slopes of parallel and perpendicular lines.
Use the slope-intercept form to write an equation of a line.
Use the slope-intercept form to graph a linear equation.
Find equations of vertical and horizontal lines.
Section 3.4 & 3.5

3. Finding the Slope of a Line Given Two Points of the Line
A key feature of a line is its slant or steepness. This measure is called the slope of the line.
Slope is the ratio of the vertical change to the horizontal change between two points as we move along the line.
Can be found on a graph by counting the vertical rise and horizontal run.
Section 3.4 & 3.5

4. Finding the Slope of a Line Given Two Points of the Line
Find the slope of the line between
A to B
Down 3  -3
Right 3  +3
B to A
Up 3  +3
Left 3  -3
The direction traveled does not matter, the slope will be the same either way.
A and C
B and C
Section 3.4 & 3.5

5. Summary of Slope
The slope of a line is always interpreted by reading the line as it moves from left to right.
Upward Line
Positive Slope
m > 0
Downward Line
Negative Slope
m < 0
Horizontal Line
Zero Slope
m = 0
Vertical Line
Undefined Slope
m does not exist
Section 3.4 & 3.5

6. Finding the Slope of a Line Given Two Points of the Line
Consider the points (1, 0) and (4, 3) in the coordinate plane.
Count the “rise” and the “run” to determine the slope of the line between the points. 3
4 – 1 3
3 – 0
Section 3.4 & 3.5

7. Finding the Slope of a Line Given Two Points of the Line
The Slope Formula
Given two points and , where , the slope of the line connecting the two points is given by the formula
Find the slope of the line connecting the given points.
(6, -2) and (5, 5) x y -5 7 -2 5 1 3 4
Section 3.4 & 3.5

8. Using the Slope-Intercept Form to Graph an Equation
Graph the line passing through the point (-2, 5) with a slope of -3.
To graph, plot the known point.
Slope is the “rise” and “run” needed to get from one point to another along a line.
Follow the slope to reach a second point.
Connect the points with a straight line.
Section 3.4 & 3.5

9. Using the Slope-Intercept Form to Graph an Equation
Through the given point, draw a line with the given slope.
1. (3, 2) m = 4
3. (2, -7) m = 0
2. (-2, -1) m = 2/7
4. x-int: -3, m = -1/2
Section 3.4 & 3.5

10. Finding the Slope of a Line Given Its Equation
Slope-Intercept Form
When a linear equation in two variables is written in slope-intercept form, , m is the slope of the line and (0, b) is the y-intercept of the line.
Find the slope and y-intercept of the line.
Equation must be written in y = mx + b
All horizontal lines have a slope of zero.
All vertical lines have undefined slope.
Section 3.4 & 3.5

11. Using the Slope-Intercept Form to Write an Equation
When a linear equation in two variables is written in slope-intercept form, , m is the slope of the line and (0, b) is the y-intercept of the line.
Find the equation of the line with y-intercept (0, 7) and slope of ½.
Find the equation of the line through the points (1, 3) and (0, 4)
Section 3.4 & 3.5

12. Finding Equations of Vertical and Horizontal Lines
Find an equation of the horizontal line through the point (1, 4).
Find an equation of the vertical line through the point (1, 4).
Section 3.4 & 3.5

13. Using the Slope-Intercept Form to Graph an Equation
If an equation is in slope-intercept form, both the slope and a point on the line are known.
Slope-Intercept Form
slope
y-intercept
(0, b)
Section 3.4 & 3.5

14. Using the Slope-Intercept Form to Graph an Equation
To graph an equation in slope-intercept form y = mx + b:
Plot the y-intercept (0, b).
Plot a second point by rising the number of units indicated by the numerator of the slope then running the number of units indicated by the denominator of the slope, m.
Draw a straight line through the points.
Find the slope and y-intercept of each line, then graph.
Section 3.4 & 3.5

15. Using the Slope-Intercept Form to Graph an Equation
Determine the slope and y-intercept, then graph.
7. 2x + y = 8
9. 4x – 3y = 9
8. 4y = -8x
10. y = 8
Section 3.4 & 3.5

16. Using the Slope-Intercept Form to Graph an Equation
Determine the slope and y-intercept, then graph.
11. 2x – y = 4
13. 3x – 4y = 4
12. x = 4
14. x = 3/2 y
Section 3.4 & 3.5

17. Slopes of Parallel and Perpendicular Lines
Parallel lines have the same slope.
Perpendicular
Perpendicular lines have slopes that are negative reciprocals, or a product of -1.
Section 3.4 & 3.5

18. Slopes of Parallel and Perpendicular Lines
Determine if the pair of lines is parallel, perpendicular, or neither.
Section 3.4