# discovering slope intercept form of a line - .web viewdiscovering slope-intercept form 2. lesson

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Project AMP Dr. Antonio R. Quesada Director, Project AMP

Page 1 of 14

1. Lesson Title: Discovering Slope-Intercept Form

2. Lesson Summary: This lesson is a review of slope and guides the students through discovering slope-intercept form using paper/pencil and graphing calculator. It includes looking at positive/negative slopes, comparing the steepness of slopes, and relating slope to real-world applications (handicapped ramps, stairs).

3. Key Words: slope, slope-intercept form, y-intercept, linear equations

4. Background knowledge:

Students are presumed to know:

how to plot points

how to find x and y intercepts

how to find slope by counting blocks from one point to another on the line

how to graph and use a table on a graphing calculator

Grade 9: Patterns, Functions and Algebra:

#2 Generalize patterns using functions and relationships (linear), and freely translate among tabular, graphical, and symbolic representations.

#6 Write and use equivalent forms of equations and inequalities in problem situations; e.g. changing a linear equation to slope-intercept form.

6. State Strand(s) and Benchmark Addressed:

Grade 8-10: Patterns, Functions, and Algebra:

B. Identify and classify functions as linear or nonlinear, and contrast their properties using

table, graphs, or equations.

E. Analyze and compare functions and their graphs using attributes, such as rate of change,

intercepts, and zeros.

J. Describe and interpret rates of change from graphical and numerical data.

7. Learning Objectives:

1. To find the slope of a line by counting horizontal and vertical distances.

2. To find x and y intercepts algebraically and by interpreting graphs.

3. To write equations in slope-intercept form.

4. To compare slopes based on steepness and direction.

5. To match linear equations to their graphs.

6. To apply slope concepts to real-world application.

8. Materials:

Graphing calculator

Ruler

9. Suggested procedures:

a. Cite the attention getter: Have you all walked up and down steps before? What concept

math courses? Over the next couple of days, we are going to revisit the concept of slope

and extend the concept further.

b. Students may be divided into groups of three/four.

10. Assessment(s): A quiz will be given to assess that the above objectives were met. The quiz and answer key are included.

DISCOVERING SLOPE INTERCEPT FORM

This lesson is a review of slope. It will guide you through discovering slope-intercept form using paper/pencil and a graphing calculator. It includes looking at positive/negative slope, comparing the steepness of slopes, and relating slope to real-world applications (handicapped ramps, stairs).

1.

rise

run

a) Plot the points ( -1, -3) and (2,3) on the grid and then connect them.

b) Name the y-intercept as a coordinate.

c) Count blocks up and then right to move from ( -1, -3) to (2,3). Up is a positive direction; right is a positive direction. Write these results in rise/run (fraction) form.

d) You have just named the slope for this line. Is the slope rising or falling?

e) Now count blocks moving from (2,3) to (-1, -3), in other words, count blocks down and then left. Down is a negative direction (what sign should you then write before your number?); left is a negative direction (what sign should you then write before your number?). Write these results in rise/run (fraction) form. You have just named the slope for this line.

f) Now write your results in proportion form (setting the two fractions equal to one another). Is this a true statement? How so?

2. a) Plot the points ( -4, 2) and (5,-1) on the grid.

b) Thinking of what you did in Problems #1, name the slope of the drawn line. In other words, how did you get from one point to the other?

c) Is the slope positive (rising) or negative (falling)? Why?

d) Now go from the opposite point to the other. Name the slope.

e) Are the slopes equivalent? Why?

Slope is a fraction that tells you how steep a line is. The numerator tells you the vertical distance and the denominator tells you the horizontal distance. We describe slope as

to help us remember this.

3. Complete the following table.

Original Equation

Rewrite as y=

x-intercept

y-intercept

Slope

y

2

-

y

1

x

2

-

x

1

a.

2y-4=x

( , 0)

( 0 , )

b.

2y+6=10x

( , 0)

( 0 , )

c.

2y+8=4x

( , 0)

( 0 , )

d.

-y+3=x

( , 0)

( 0 , )

e.

y-1=-4x

( , 0)

( 0 , )

f.

4y-20=-x

( , 0)

( 0 , )

4. In each row, compare the slope and the numbers in the equation of the form y=. What do you notice?

5. In each row, compare the y-intercept and numbers in the equation of the form y=. What do you notice?

6. Make some conclusions about what you noticed in comparing slope and y-intercept with the equations written in y= form.

7. Extension questions:

a. Given the equation y = 2x + 5, where would the graph of this equation cross the y-axis? What is the slope of this line?

b. Graph the equation in part a on your calculator and compare your results to the graph.

c. Given the equation y = 5 + 2x, where would the graph of this equation cross the y-axis? What is the slope of this line?

d. Graph the equation in part c in your calculator on the same grid as part a.

e. How many lines do you have on your calculator?

f. What happened? Why did this happen?

g. What arithmetic property of real numbers have you just rediscovered? Give another example using this property. State the y-intercept and the slope. What can you conclude?

h. Given the equation y = 3x, where would the graph of this equation cross the y-axis? Why did you say what you wrote? Check your graph with the graphing calculator.

Equations in the form y=mx+b are equations in slope-intercept form, where m is the slope and b is the y-intercept.

8. Graph the equations a, b, and c from the chart in question 3 in your calculator and sketch the graphs below.

9. What do all of the graphs in question 8 have in common? How does this relate to the slope?

10. What do you notice about how the slope relates to the steepness of the lines in question 8?

11. Graph equations d, e, and f from the chart in question 3 in your calculator and sketch below.

12. What do all of the graphs in question 11 have in common? How does this relate to the slope?

13. What do you notice about how the slope relates to the steepness of the lines in question 11?

14. For each pair of equations, circle the equation of the line that would be steeper when graphed. If they have the same steepness, circle both of them.

y

=

3

x

-

1

or

y

=

2

x

-

3

y

=

1

2

x

+

3

or

y

=

-

4

x

-

8

y

=

5

x

+

1

or

y

=

-

5

x

+

3

3

y

+

9

=

6

x

or

2

y

-

12

=

-

8

x

15. Rewrite each of the following equations in slope-intercept form; then match each equation to its graph.

1. x=y

2. -2y+10=x

3. 3y+3=2x

4. x=y-4

5. y+2x=1

6. y+x=1

CHECK FOR UNDERSTANDING:

a. In y=mx+b, m represents the ________________________ of the line.

b. In y=mx+b, b represents the _________________________ of the line.

c. Rise is the _________________________ distance.

d. Run is the _________________________ distance.

e. Create three equations in slope-intercept form.

y=_____________y=___________y=___________

f. Circle the slope in each equation.

g. Box the y-intercept in each equation.

h. Graph each equation in your calculator and sketch below.

i. For each equation, name two points that are on each line, other than the y-intercept.

Equation #1:(_____,_____), (_____,_____)

Equation #2:(_____,_____), (_____,_____)

Equation #3:(_____,_____), (_____,_____)

j. Look at the table feature in your calculator to verify that your points are on the line.

k. Create two more equations. Circle the slope and box the y-intercept. Graph each equation in the calculator and sketch in the space below. Notice that graph paper has not been provided. (

EXTENSION:

The building codes and safety standards for slope are listed below:

Maximum Slope

Ramps-wheelchair

0.125

Ramps-walking

0.3

Driveway or street parking

0.22

Stairs

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