algebra 2 unit 3.1

UNIT 3.1 SOLVING SYSTEMS UNIT 3.1 SOLVING SYSTEMS USING TABLES AND GRAPHSUSING TABLES AND GRAPHS

Warm UpUse substitution to determine if (1, –2) is an element of the solution set of the linear equation.

1. y = 2x + 1 2. y = 3x – 5 no yes

Write each equation in slope-intercept form.3. 2y + 8x = 6 4. 4y – 3x = 8

y = –4x + 3

Solve systems of equations by using graphs and tables.

Classify systems of equations, and determine the

number of solutions.

Objectives

system of equationslinear systemconsistent systeminconsistent systemindependent systemdependent system

Vocabulary

A system of equations is a set of two or more equations containing two or more variables. A linear system is a system of equations containing only linear equations.

Recall that a line is an infinite set of points that are solutions to a linear equation. The solution of a system of equations is the set of all points that satisfy each equation.

On the graph of the system of two equations, the solution is the set of points where the lines intersect. A point is a solution to a system of equation if the x- and y-values of the point satisfy both equations.

Use substitution to determine if the given ordered pair is an element of the solution set for the system of equations.

Example 1A: Verifying Solutions of Linear Systems

(1, 3); x – 3y = –8

3x + 2y = 9

Substitute 1 for x and 3for y in each equation.

Because the point is a solution for both equations, it is a solution of the system.

3x + 2y = 9

3(1) +2(3) 9

9 9

x – 3y = –8

(1) –3(3) –8

–8 –8


Example 1B: Verifying Solutions of Linear Systems

(–4, ); x + 6 = 4y

2x + 8y = 1

x + 6 = 4y

(–4) + 6

2 2

Because the point is not a solution for both equations, it is not a solution of the system.

2x + 8y = 1

2(–4) + 1

–4 1

Substitute –4 for x andfor y in each equation. x

1

2

Check It Out! Example 1a


(4, 3); x + 2y = 10

3x – y = 9

Because the point is a solution for both equations, it is a solution of the system


x + 2y = 10

(4) + 2(3) 10

10 10 9

3(4) – (3)

3x – y = 9

9

9

Check It Out! Example 1b


(5, 3); 6x – 7y = 1

3x + 7y = 5


Because the point is not a solution for both equations, it is not a solution of the system.

5

3(5) + 7(3)

3x + 7y = 5

5

36 x

6x – 7y = 1

6(5) – 7(3) 1

9 1x

Recall that you can use graphs or tables to find some of the solutions to a linear equation. You can do the same to find solutions to linear systems.

Use a graph and a table to solve the system. Check your answer.

Example 2A: Solving Linear Systems by Using Graphs and Tables

2x – 3y = 3

y + 2 = x

Solve each equation for y.y= x – 2

y= x – 1

On the graph, the lines appear to intersect at the ordered pair (3, 1)

Example 2A Continued

Make a table of values for each equation. Notice that when x = 3, the y-value for both equations is 1.

x y

0 –2

1 – 1

2 0

3 113

2

1

–10

yx

y= x – 2 y= x – 1

The solution to the system is (3, 1).

Example 2A Continued


Example 2B: Solving Linear Systems by Using Graphs and Tables

x – y = 2

2y – 3x = –1

Solve each equation for y.y = x – 2

y =

Example 2B Continued

Use your graphing calculator to graph the equations and make a table of values. The lines appear to intersect at (–3, –5). This is the confirmed by the tables of values.

Check Substitute (–3, –5) in the original equations to verify the solution.

The solution to the system is (–3, –5).

2(–5) – 3(–3)

2y – 3x = –1

–1

–1

–1

(–3) – (–5)

2

x – y = 2

2

2


2y + 6 = x

4x = 3 + y


Solve each equation for y.y= 4x – 3

y= x – 3

On the graph, the lines appear to intersect at the ordered pair (0, –3)

Check It Out! Example 2a Continued

Make a table of values for each equation. Notice that when x = 0, the y-value for both equations is –3.

3

–22

1

–30

yx x y

0 –3

1 1

2 5

3 9

The solution to the system is (0, –3).

y = 4x – 3y = x – 3

Check It Out! Example 2a Continued


x + y = 8

2x – y = 4


y = 2x – 4

y = 8 – xSolve each equation for y.

On the graph, the lines appear to intersect at the ordered pair (4, 4).

Check It Out! Example 2b Continued

Make a table of values for each equation. Notice that when x = 4, the y-value for both equations is 4.

x y

1 –2

2 0

3 2

4 4

x y

1 7

2 6

3 5

4 4

y = 2x – 4y= 8 – x

The solution to the system is (4, 4).

Check It Out! Example 2b Continued

Use a graph and a table to solve each system. Check your answer.

y – x = 5

3x + y = 1

y= –3x + 1

y= x + 5

Check It Out! Example 2c

Solve each equation for y.

On the graph, the lines appear to intersect at the ordered pair (–1, 4).

Check It Out! Example 2c Continued

Make a table of values for each equation. Notice that when x = –1, the y-value for both equations is 4.

x y

–1 4

0 1

1 –2

2 –5

x y

–1 4

0 5

1 6

2 7

The solution to the system is (–1, 4).

y= –3x + 1y= x + 5

Check It Out! Example 2c Continued

The systems of equations in Example 2 have exactly one solution. However, linear systems may also have infinitely many or no solutions. A consistent system is a set of equations or inequalities that has at least one solution, and an inconsistent system will have no solutions.

You can classify linear systems by comparing the slopes and y-intercepts of the equations. An independent system has equations with different slopes. A dependent system has equations with equal slopes and equal y-intercepts.

Classify the system and determine the number of solutions.

Example 3A: Classifying Linear System

x = 2y + 6

3x – 6y = 18


The system is consistent and dependent with infinitely many solutions.

The equations have the same slope and y-intercept and are graphed as the same line.

y = x – 3

y = x – 3


Example 3B: Classifying Linear System

4x + y = 1

y + 1 = –4x


The system is inconsistent and has no solution.

y = –4x + 1

y = –4x – 1

The equations have the same slope but different y-intercepts and are graphed as parallel lines.

Check A graph shows parallel lines.

Example 3B Continued


7x – y = –11

3y = 21x + 33


The system is consistent and dependent with infinitely many solutions.

The equations have the same slope and y-intercept and are graphed as the same line.


y = 7x + 11

y = 7x + 11

Classify each system and determine the number of solutions.

x + 4 = y

5y = 5x + 35


The system is inconsistent with no solution.

The equations have the same slope but different y-intercepts and are graphed as parallel lines.


y = x + 4

y = x + 7

City Park Golf Course charges $20 to rent golf clubs plus $55 per hour for golf cart rental. Sea Vista Golf Course charges $35 to rent clubs plus $45 per hour to rent a cart. For what number of hours is the cost of renting clubs and a cart the same for each course?

Example 4: Summer Sports Application

Example 4 Continued

Let x represent the number of hours and y represent the total cost in dollars.

City Park Golf Course: y = 55x + 20

Sea Vista Golf Course: y = 45x + 35

Because the slopes are different, the system is independent and has exactly one solution.

Step 1 Write an equation for the cost of renting clubsand a cart at each golf course.

Step 2 Solve the system by using a table of values.

x y

0 20

47.5

1 75

102.5

2 120

x y

0 35

57.5

1 80

102.5

2 125

y = 55x + 20 y = 45x + 35Use increments of to represent 30 min.

When x = , the y-values are both 102.5. The cost of renting clubs and renting a cart for hours is $102.50 at either company. So the cost is the same at each golf course for hours.

Example 4 Continued

Check It Out! Example 4

Ravi is comparing the costs of long distance calling cards. To use card A, it costs $0.50 to connect and then $0.05 per minute. To use card B, it costs $0.20 to connect and then $0.08 per minute. For what number of minutes does it cost the same amount to use each card for a single call?

Step 1 Write an equation for the cost for each of the different long distance calling cards.Let x represent the number of minutes and y represent the total cost in dollars.

Card A: y = 0.05x + 0.50 Card B: y = 0.08x + 0.20

Check It Out! Example 4 Continued

x y

1 0.28

5 0.60

10 1.00

15 1.40

x y

1 0.55

5 0.75

10 1.00

15 1.25

y = 0.05x + 0.50 y = 0.08x + 0.20

Step 2 Solve the system by using a table of values.

When x = 10 , the y-values are both 1.00. The cost of using the phone cards of 10 minutes is $1.00 for either cards. So the cost is the same for each phone card at 10 minutes.

Lesson Quiz: Part I

Use substitution to determine if the given ordered pair is an element of the solution set of the system of equations.

x + y = 2

y + 2x = 5

x + 3y = –9

y – 2x = 4no yes

1. (4, –2) 2. (–3, –2)

Solve the system using a table and graph. Check your answer.

3.x + y = 1

3x –2y = 8

(2, –1)

Lesson Quiz: Part IIClassify each system and determine the number of solutions.

4. 5.–4x = 2y – 10

y + 2x = –10

y + 2x = –10

y + 2x = –10

inconsistent; none consistent, dependent; infinitely many

6. Kayak Kottage charges $26 to rent a kayak plus $24 per hour for lessons. Power Paddles charges $12 for rental plus $32 per hour for lessons. For what number of hours is the cost of equipment and lessons the same for each company?

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algebra 2 unit 3.1

Education

linear equations

systems of equations

system substitute

solution set

solutions of linear

given ordered pair

b use substitution

infinite set of points