Mathematics: Quarter 1 - Module 9
Mathematics: Quarter 1 - Module 9
NOT
Mathematics
Quarter 1 - Module 9
Graphing Linear Equations
in Two Variables
Mathematics - Grade 8
Alternative Delivery Mode
Quarter 1 – Module 9: Graphing Linear Equations in Two Variables
First Edition, 2020
Republic Act 8293, section 176 states that: No copyright shall subsist
in any work of the Government of the Philippines. However, prior approval of
the government agency or office wherein the work is created shall be necessary
for exploitation of such work for profit. Such agency or office may, among other
things, impose as a condition the payment of royalty.
Mathematics
Quarter 1 - Module 9
Graphing Linear Equations
in Two Variables
This page is intentionally blank
Table of Contents
What I Know…………………………………………………………………………………………..iii
Lesson 1:
Graphing Linear Equations in Two Variables …………………………...1
What I Need to Know…………………………………………………………….1
Summary……………………………………………………………………………………14
Assessment: (Post-Test)………………………………………………………………...14
Key to Answers……………………………………………………………………………………17
References………………………………………………………………………………………….20
This page is intentionally blank
What This Module is About
This module discusses the four (4) methods on how to graph linear equations
in two variables. Each method will be discussed with a given example.
You are expected at the end of this module to sketch the graphs of the linear
equations in two variables.
i
Icons of this Module
What I Need to This part contains learning objectives that
Know are set for you to learn as you go along the
module.
ii
What I Know
Pre-Assessment
Directions: Read and understand each question carefully and write the letter of your
answer in your answer sheet.
1. The following are the methods on how to graph a line, except
a. using given intercepts c. using slope and a point
b. using given points d. using random ordered pairs
2. Which of the following is a linear equation in two variables?
a. 3x2 = y c. 8x + 9y = 3z
b. y = 7x – 7 d. x + y
3. The graph of a linear equation is a ________.
a. parabola c. line
b. curve d. broken line
4. The graph of the points (3, 5) and (7, 1) is ______.
a. 7
6
c. 7
5
5
4
4
3
3
2
2
1 1 2 3 4 5 6 7 8
1 1 2 3 4 5 6 7 8 -5 -4 -3 -2 -1 -1
-5 -4 -3 -2 -1 -1
-2
-2
-3
-3
-4
-4
-5
-5
7 6
b. 6
4
d. 5
3 2
2 1 1 2 3 4 5 6 7 8
-5 -4 -3 -2 -1 -1
1 1 2 3 4 5 6 7 8
-5 -4 -3 -2 -1 -1 -2
-2 -3
-3 -4
-4 -5
-5
iii
For numbers 11 to 15, identify the linear equation. Refer your answers on the
given graph.
11. -10
-9
a. y = -7x -7
-8
3
-7
-6 b. y = − 𝑥 − 3
-5 7
-4
7
-3
-2 c. 𝑦 = − 𝑥 − 7
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
-1 3
-1
-2
1 2 3 4 5 6 7 8 9
d. y = -x – 3
-3
-4
-5
-6
-7
-8
-9
-10
12. a. y = x + 6
b. y = -x -6
-10
-9
-8
-7
-6
-5
c. y = -x + 6
d. y = x – 6
-4
-3
-2
-1
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
1 2 3 4 5 6 7 8 9 10
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
13. -10
a. y = x + 3
b. y = x – 3
-9
-8
-7
c. y = -x – 3
-6
-5
-4
-3
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
-2
-1 d. y = -x + 3
1 2 3 4 5 6 7 8 9 10
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
10
14. 9
8
7
a. y = 7x + 7
6
5
4
b. y = x + 2
3
2
2
1 c. 𝑦 = − 𝑥 + 2
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
1 2 3 4 5 6 7 8 9 10
7
-1
7
-2
-3 d. 𝑦 = − 𝑥 + 7
-4 2
-5
-6
-7
-8
-9
15. 10 a. y = -4
9
8 b. x = -4
7
6 c. y = 4
5
4
3
d. x = 4
2
1
-8 -7 -6 -5 -4 -3 -2 -1
1 2 3 4 5 6 7
-1
-2
-3
-4
-5
-6
-7
-8
-9
iv
This page is intentionally blank
Graphing Linear Equations
Lesson in Two Variables
1
What I Need to Know
In the previous module, you have learned that there are many ways in
representing functions. One of which is through an equation. A linear equation in two
variables can be written in its standard form Ax + By = C or slope-intercept form
y = mx + b. It can also be graphed using the following methods:
a. using any two points;
b. using the x and y intercepts;
c. using the slope and y - intercept; and
d. using the slope and a given point.
What’s New
5
Activity 1 Describe Me! 4
-3
-5
1. x – intercept 4. run
2. y – intercept 5. slope
3. rise 6. trend
1
What Is It
Activity 1 lets you describe the graph of a linear equation in two variables. Its
graph is a line, and a line is created using two points. This leads to the first method of
graphing a linear equation in two variables which is using two points.
Illustrative Example
Graph the linear equation in two variables y = x + 2 using two points.
Step Solution
1 Let x = 1 and x = - 2.
2 If x = 1, then If x = - 2, then
y=x+2 y=x+2
y=1+2 y=-2+2
y=3 y= 0
Hence, the first point Hence, the second point
(solution) is (1, 3). (solution) is (- 2, 0).
2
4
What’s More
1. y = - 3x + 4
x=2 x = -1
y = - 3x + 4 y = - 3x + 4
y = - 3(2) + 4 y = - 3(-1) + 4
y=-6+4 y=3+4
y=-2 y=7
(2, -2) (- 1, 7)
Graph created from https://www.desmos.com/calculator.
2. x – y = 5
x=3 x=-2
3
3. 3x + 4y = 0
x=4 x=-3
4. 4x – 2y = 6
x=4 x=-3
What Is It
The x – intercept is the abscissa of the coordinates of the point (a, 0) where
the graph intersects the x – axis while the y – intercept is the ordinate of the
coordinates of the point (0, b) where the graph intersects the y – axis. The next method
of graphing makes use of the intercepts.
4
Illustrative Example
Step Solution
1 Let x = 0,
2x – y = 4
2(0) – y = 4
–y=4
y = - 4. Hence, (0, - 4).
2 Let y = 0,
2x – y = 4
2x – 0 = 4
2x = 4
x=2 Hence, (2, 0).
3
5
What’s More
Graph the linear equations in two variables using the x – intercept and y –
intercept. The first item serves as an example, answer numbers 2 – 4.
1. x + y = 8
x – intercept: a = 8 y – intercept: b = 8
x+y=8 x+y=8
x+0=8 0+y=8
x=8 y=8
(8, 0) (0, 8)
3
2. y = x
4
x – intercept: a = y – intercept: b =
3. 5x = 20 – 2y
x – intercept: a = y – intercept: b =
4. 3x + 6y + 9 = 0
x – intercept: a = y – intercept: b =
6
What Is It
You have learned that the standard form of the linear equation of two variables
𝑨𝒙 + 𝑩𝒚 = 𝑪 can be rewritten in its slope-intercept form which is 𝒚 = 𝒎𝒙 + 𝒃. The third
method of graphing uses the slope and y – intercept.
Steps in graphing linear equations in two variables using the slope and
y - intercept.
1. Write the equation in the slope-intercept form 𝒚 = 𝒎𝒙 + 𝒃.
2. Identify the slope m and y – intercept b.
3. Plot the point (0, b) in the rectangular coordinate system.
rise
4. From the point (0, b), plot another point using the slope 𝒎= .
run
A third point is use for checking.
5. Connect the points to form a straight line.
Illustrative Example
Graph the linear equation in two variables 4𝑥 + 5𝑦 = 20 using the slope and
y - intercept.
Step Solution
1 4x + 5y = 20
5y = - 4x + 20
4
y = − x+4
5
2 4
𝑚 =− and b = 4
5
3
or
7
5
What’s More
1. 3x + 2y = 18
slope: m = -
3 y – intercept: b = 9
2
3x + 2y = 18
2y = - 3x + 18
3
y=- x+9
2
2. 2𝑥 − 5𝑦 = 15
slope: m = y – intercept: b =
8
3. x + 4y = - 4
slope: m = y – intercept: b =
4. y = 7x + 9
slope: m = y – intercept: b =
What Is It
The fourth method of graphing makes use the slope and a point on the line.
The point is a solution of the linear equation in two variables.
Steps in graphing linear equations in two variables using the slope and
a point on a line.
1. Write the equation in the slope-intercept form 𝒚 = 𝒎𝒙 + 𝒃 and identify the
rise
slope 𝒎= .
run
2. To find a point, assign a value for x and substitute it in the equation to solve
for y. You will have point (x, y).
3. Plot point (x, y) in the rectangular coordinate plane.
rise
4. From point (x, y), plot another point using the slope 𝒎= .
run
A third point is use for checking.
5. Connect the points to form a straight line.
9
Illustrative Example
Graph the linear equation in two variables -8x + 6y = - 12 using the slope and
a point.
Step Solution
1 -8x + 6y = - 12
6y = 8x - 12
4
y= x –2
3
4
slope: 𝑚 =
3
y=4–2
y=2
(3, 2) (3, 2)
3
10
5
What’s More
For each linear equation in two variables, find the slope, a point and then graph.
The first item serves as an example, answer numbers 2 – 4.
1. x - 3y = 15
x - 3y = 15 Let x = 6
- 3y = - x + 15 1
y= x–5
1 3
y= x–5 1
3 y= (6) –5
3
6
1 y= –5
slope: m = 3
3 y=2–5
y=-3
(6, -3)
2. y = 5x + 2
Slope: m = Let x = 1
11
3. 2x – y = 2
slope: m = Let x = 2
4. 2x + 3y = -3
slope: m = Let x = 3
Activity 6 Generalization
Fill in the diagram below the steps in graphing linear equations in two variables
using the four (4) different methods.
Using the
Using Slope &
a point
Intercepts
12
What I Can Do
Activity 7 Light Me Up
Description: This activity will enable you to solve real-life problems involving linear
functions.
Directions: Consider the situation below and answer the questions that follow.
Zeke lights a 9 inches long candle. He records the length of the candle,
y represents the length while x represents the hours.
13
Summary
A linear equation in two variables can be graphed using:
Assessment: (Post-Test)
Directions: Read and understand each question carefully and write the letter of your
answer in your answer sheet.
3. In graphing linear equations in two variables using slope and y-intercept form,
if m > 0, the graph is a line that rises from _______ to _______.
a. right, left c. left, right
b. Top, bottom d. none of the above
4. In graphing linear equations in two variables using slope and y-intercept form,
if m < 0, the graph is a line that rises from _______ to _______.
a. top, bottom c. right, left
b. left, right d. none of the above
14
5. State the four (4) methods on how to graph linear equations in two variables.
For numbers 6 to 10, identify the linear equation. Refer your answers on the
given graph.
3
6. a. 𝑦 = 𝑥 + 3
2
b. 𝑦 = 𝑥 + 3
c. 𝑦 = −2𝑥 – 2
2
d. 𝑦 = 𝑥 –2
3
7. a. y = -4
b. x = -4
c. y = 4
d. x = 4
8. a. y = 7x + 7
b. y = x + 2
2
c. 𝑦 = − 𝑥 + 2
7
7
d. 𝑦 = − 𝑥 + 7
2
9. a. y = x -3
b. y = -x -3
c. 𝑦 = 𝑥 + 3
d. 𝑦 = −𝑥 + 3
10. a. y = x + 6
b. y = -x – 6
c. y = -x + 6
d. y = x – 6
15
For numbers 11 to 15. Tell whether the statement is TRUE or FALSE.
11. The graph of 0x + 1y = 8 is a horizontal line.
12. The graph of the equation x = -6 is a vertical line.
13. The graph of a linear equation in two variables is a line.
14. Given one point, a graph of a linear equation can be sketched.
15. In the slope-intercept form of an equation, b represents the y-intercept.
16
17
Pre-Assessment:
1. d 6. c 11. a
2. b 7. c 12. b
3. c 8. a 13. b
4. a 9. c 14. c
5. b 10. b 15. b
Lesson 1
Activity 1 Describe Me!!!
1. x-intercept: -3 4. run: 3
2
2. y-intercept: 2 5. slope:
3
3. rise: 2 6. trend: increasing
Activity 2 Sketch Me (Part 1)
2. (3, -2) (-2, -7) 3. (4, -3) (-3, 9/4)
4. (4, 5) (-3, -9)
Key to Answers
18
Activity 3 Sketch Me (Part 2)
2. (0,0) 3. (0,10) (4, 0) 4. (0,-3/2) (-3, 0)
Activity 4 Sketch Me (Part 3)
2. m = 2/5 b = -3 3. m = -1/4 b = -1 4. m = 7 b = 9
Activity 5 Sketch Me (Part 4)
2
2. m = 5; (1,7) 3. m = 5; (2,2) 4. m = − ; (3,-3)
3
19
Activity 6
Steps in graphing linear equations in two Steps in graphing linear equations in two
variables using x – intercept and variables using the slope and
y - intercept. y - intercept.
1. Solve for y – intercept by letting x = 0 to have 1. Write the equation in the slope-intercept form
a point (0, b). 𝒚 = 𝒎𝒙 + 𝒃.
2. Solve for x – intercept by letting y = 0 to have 2. Identify the slope m and y – intercept b.
a point (a, 0). 3. Plot the point (0, b) in the rectangular
3. Plot the two points in the rectangular coordinate system.
coordinate system. 4. From the point (0, b), plot another point using
4. Connect the two points to form a straight line. rise
the slope 𝒎= .
run
A third point is use for checking.
5. Connect the points to form a straight line.
Steps in graphing linear equations in two Steps in graphing linear equations in two
variables using x – intercept and variables using the slope and
y - intercept. a point on a line.
1. Solve for y – intercept by letting x = 0 to have 1. Write the equation in the slope-intercept form
a point (0, b). rise
𝒚 = 𝒎𝒙 + 𝒃 and identify the slope 𝒎= .
run
2. Solve for x – intercept by letting y = 0 to have
2. To find a point, assign a value for x and
a point (a, 0).
substitute it in the equation to solve for y. You
3. Plot the two points in the rectangular
will have point (x, y).
coordinate system.
3. Plot point (x, y) in the rectangular coordinate
4. Connect the two points to form a straight line.
plane.
4. From point (x, y), plot another point using the
rise
slope 𝒎= .
run
A third point is use for checking.
5. Connect the points to form a straight line.
Activity 7
1. The dependent variable is the height of the candle because it depends on the
number of hours the candle is burning.
2. The independent variable is the number of hours the candle is burning because
it controls the height of the burning candle.
3. Yes. It represents a line.
4. The y-intercept of the line is 9.
5. The slope is -2.
6. The equation is y = 9x – 2.
Post-Test
1. d 6. c 11. False
2. b 7. c 12. True
3. c 8. b 13. True
4. c 9. d 14. False
5. Using two points, 10. d 15. True
x- and y-intercept,
slope and one point,
and slope and y-intercept.
References:
Abuzo, Emmanuel, Merden Bryant, Jem Boy Cabrella, Belen Caldez, Melvin
Callanta, Anastacia Proserfina Castro, Alicia Halabaso, Sonia Javier, Roger
Nocom, and Concepcion Ternida. Mathematics Learner's Module 8. 1st ed.
Reprint, Department of Education, 2013.
"Graphs Of Linear Equation In Two Variables - Module 2". Word, 2014. 6485. DepEd
Learning Portal.
Graph Equations Using Intercepts. Ebook. Kuta Software. Accessed 19 May 2020.
https://1.cdn.edl.io/1sCN5pFW8K6u2nVRJKjKVBd2Iq1iIhP4xPj8cFhQC4rUW
Uio.pdf
20
Khan Academy. Graphing Using X- And Y-Intercepts | Graphing Lines And Slope |
Algebra Basics | Khan Academy. Video, 2011.
https://www.youtube.com/watch?v=6m642-2D3V4.
Math Wizard. Graph A Linear Equation Given Any Two Points. Video, 2020.
https://www.youtube.com/watch?v=vwo1p1t2kxA.
21
For inquiries and feedback, please write or call:
22