Using
Graphs
and
Tables
Using
Graphs
and
Tables
3-1
3-1 to Solve Linear Systems
to Solve Linear Systems
Warm Up
Lesson Presentation
Lesson Quiz
Holt
Algebra
Holt
Algebra
22
3-1
Using Graphs and Tables
to Solve Linear Systems
Warm Up
Use substitution to determine if (1, –2) is an
element of the solution set of the linear
equation.
1. y = 2x + 1 no
2. y = 3x – 5 yes
Write each equation in slope-intercept form.
4. 4y – 3x = 8
3. 2y + 8x = 6
y = –4x + 3
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Objectives
Students will solve systems of equations by using graphs
and tables, classify systems of equations, and determine
the number of solutions a system has.
Essential Questions
How can I find the solution to a system of linear
equations? What does it mean if my answer doesn't
have a point in common?
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Vocabulary
system of equations
linear system
consistent system
inconsistent system
independent system
dependent system
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Substitution is another way
to say replace the variables
with the point values
to see if the equation stays true.
(3,11) for f(x) = 3x+2 --->
Holt Algebra 2
3(3) + 2 = 11
3-1
Using Graphs and Tables
to Solve Linear Systems
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.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
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.
Satisfy is another way to say the x and y work in
all equations in the system. We check this by
substituting the values into the equation.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Many systems of equations 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.
(intersecting lines OR overlapping lines, one
on top of the other)
An inconsistent system will have no
solutions. (parallel lines that never intersect)
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
You can classify linear systems by comparing the
slopes and y-intercepts of the equations.
An independent system has equations with different
slopes. (intersecting lines)
A dependent system has equations with equal
slopes and equal y-intercepts. (overlapping lines)
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Now you let’s try
some!
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 1A: Verifying Solutions of Linear Systems
Use substitution to determine if the given
ordered pair is an element of the solution set
for the system of equations.
(1, 3);
x – 3y = –8
3x + 2y = 9
x – 3y = –8
3x + 2y = 9
(1) –3(3) –8
3(1) +2(3) 9
–8
–8 
Substitute 1 for x and 3
for y in each equation.
9
9
Because the point is a solution for both equations, it
is a solution of the system.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 1B: Verifying Solutions of Linear Systems
Use substitution to determine if the given ordered
pair is an element of the solution set for the
system of equations.
x + 6 = 4y
(–4, );
2x + 8y = 1
x + 6 = 4y
(–4) + 6
2
2
2x + 8y = 1
Substitute –4 for x and
for y in each equation.
2(–4) +
1
–4
1x
Because the point is not a solution for both equations, it
is not a solution of the system.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 1a
Use substitution to determine if the given ordered
pair is an element of the solution set for the
system of equations.
(4, 3);
x + 2y = 10
3x – y = 9
3x – y = 9
x + 2y = 10
(4) + 2(3) 10
10
10 
Substitute 4 for x and 3
for y in each equation.
3(4) – (3)
9
9
9 
Because the point is a solution for both equations, it
is a solution of the system
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 1b
Use substitution to determine if the given ordered
pair is an element of the solution set for the
system of equations.
(5, 3);
6x – 7y = 1
3x + 7y = 5
6x – 7y = 1
3x + 7y = 5
6(5) – 7(3) 1
9
1x
3(5) + 7(3)
Substitute 5 for x and 3
for y in each equation.
36
5
5x
Because the point is not a solution for both equations, it
is not a solution of the system.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 2A: Solving Linear Systems by Using Graphs
and Tables
Use a graph and a table to solve the system.
Check your answer.
2x – 3y = 3
y+2=x
Solve each equation for y.
y=
x–1
y= x – 2
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 2A Continued
On the graph, the lines
appear to intersect at
the ordered pair (3, 1);
this is the solution to
the system.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 2A Continued
y=
Make a table of values
for each equation.
Notice that when x = 3,
the y-value for both
equations is 1.
The solution to the
system is (3, 1).
Holt Algebra 2
x
0
x–1
x
y
0
–2
1
1
–1
2
2
0
3
1
3
y
–1
y= x – 2
1
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 2B: Solving Linear Systems by Using Graphs
and Tables
Use a graph and a table to solve the system.
Check your answer.
x–y=2
2y – 3x = –1
Solve each equation for y.
Holt Algebra 2
y=x–2
y=
Using Graphs and Tables
to Solve Linear Systems
3-1
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.
The solution to the system is (–3, –5).
Check Substitute (–3, –5) in the original
equations to verify the solution.
x–y = 2
(–3) – (–5)
2
Holt Algebra 2
2y – 3x = –1
2
2
2(–5) – 3(–3) –1

–1
–1 
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2a
Use a graph and a table to solve the system.
Check your answer.
2y + 6 = x
4x = 3 + y
Solve each equation for y.
y=
x–3
y= 4x – 3
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2a Continued
On the graph, the
lines appear to
intersect at the
ordered pair (0, –3)
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2a Continued
y=
x–3
y = 4x – 3
Make a table of values
for each equation.
Notice that when x = 0,
the y-value for both
equations is –3.
x
y
x
y
0
–3
0
–3
1
1
The solution to the
system is (0, –3).
2
2
5
3
9
1
3
Holt Algebra 2
–2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2b
Use a graph and a table to solve the system.
Check your answer.
x+y=8
2x – y = 4
Solve each equation for y.
y=8–x
y = 2x – 4
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2b Continued
On the graph, the
lines appear to
intersect at the
ordered pair (4, 4).
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2b Continued
y= 8 – x
y = 2x – 4
Make a table of values
for each equation.
Notice that when x = 4,
the y-value for both
equations is 4.
x
y
x
y
1
7
1
–2
2
6
2
0
The solution to the
system is (4, 4).
3
5
3
2
4
4
4
4
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2c
Use a graph and a table to solve each system.
Check your answer.
y–x=5
3x + y = 1
Solve each equation for y.
y= x + 5
y= –3x + 1
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2c Continued
On the graph, the
lines appear to
intersect at the
ordered pair (–1, 4).
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 2c Continued
y= x + 5
Make a table of values
for each equation.
Notice that when
x = –1, the y-value for
both equations is 4.
The solution to the
system is (–1, 4).
Holt Algebra 2
y= –3x + 1
x
y
x
y
–1
4
–1
4
0
5
0
1
1
6
1
–2
2
7
2
–5
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 3A: Classifying Linear System
Classify the system and determine the number
of solutions.
x = 2y + 6
3x – 6y = 18
Solve each equation for y.
y=
x–3
y=
x–3
The equations have
the same slope and
y-intercept and are
graphed as the same
line.
The system is consistent and dependent with infinitely
many solutions.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 3B: Classifying Linear System
Classify the system and determine the number
of solutions.
4x + y = 1
y + 1 = –4x
y = –4x + 1
Solve each equation for y.
y = –4x – 1
The equations have
the same slope but
different y-intercepts
and are graphed as
parallel lines.
The system is inconsistent and has no solution.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 3B Continued
Check A graph shows parallel lines.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 3a
Classify the system and determine the number
of solutions.
7x – y = –11
3y = 21x + 33
y = 7x + 11
Solve each equation for y.
y = 7x + 11
The equations have
the same slope and
y-intercept and are
graphed as the same
line.
The system is consistent and dependent with infinitely
many solutions.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 3b
Classify each system and determine the
number of solutions.
x+4=y
5y = 5x + 35
y=x+4
Solve each equation for y.
y=x+7
The equations have
the same slope but
different y-intercepts
and are graphed as
parallel lines.
The system is inconsistent with no solution.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 4: Summer Sports Application
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?
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 4 Continued
Step 1 Write an equation for the cost of renting clubs
and a cart at each golf course.
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.
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 4 Continued
Step 2 Solve the system by using a table of values.
Use increments of
represent 30 min.
When x =
, the yvalues 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.
Holt Algebra 2
to
y = 55x + 20
x
0
y
20
y = 45x + 35
x
0
57.5
47.5
1
75
1
120
80
102.5
102.5
2
y
35
2
125
3-1
Using Graphs and Tables
to Solve Linear Systems
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
Holt Algebra 2
Card B: y = 0.08x + 0.20
3-1
Using Graphs and Tables
to Solve Linear Systems
Check It Out! Example 4 Continued
Step 2 Solve the system by using a table of values.
When x = 10 , the yvalues 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.
Holt Algebra 2
y = 0.05x + 0.50 y = 0.08x + 0.20
x
y
x
y
1
0.55
1
0.28
5
0.75
5
0.60
10
1.00
10
1.00
15
1.25
15
1.40
3-1
Using Graphs and Tables
to Solve Linear Systems
186
Holt Algebra 2