Transcript SolvingLinearSystemspt1

3-1
Using Graphs and Tables
to Solve Linear Systems
Objectives
Solve systems of equations by using graphs and
tables.
Classify systems of equations, and determine the
number of solutions.
Holt Algebra 2
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.
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
1
(–4, );
2
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
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.
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 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)
Holt Algebra 2
3-1
Using Graphs and Tables
to Solve Linear Systems
Example 2B: Solving Linear Systems by Using Graphs
and Tables
Use a graph 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
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.
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. A dependent system has equations with
equal slopes and equal y-intercepts.
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
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
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 calculator.
You can use a table
to check your answer. y = 55x + 20
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
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