Chapter 7.5
Graphing Systems of Inequalities
Lesson Objective: NCSCOS 2.01
Students will know how to graph a system of linear
inequalities
Graphing Systems of Inequalities
Graph the line 4x – 2y > 6
We can start this problem as if it were an equals sign
First we have to put the equation in slope-intercept
form (y= mx + b) in order to graph it
Graphing Systems of Inequalities
Subtract 4x from both
sides
I always write the x
first so it looks like my
formula
Divide both sides by
-2
Don’t forget, the sign
flips when you divide
by a negative!
Graphing Systems of Inequalities
In order to graph, we
begin with the b
-3 means this line passes
through the y-axis at -3
Put a point at (0, -3)
Graphing Systems of Inequalities
We then need to use the
slope to find the next
point
The slope as a fraction is
Y’s are on top, and they
make the point go up and
down
2
1
Graphing Systems of Inequalities
Since the 2 is positive we
move up 2
The bottom number is
the x value
This makes the point
move left and right
Since the 1 is positive we
move one to the right
Graphing Systems of Inequalities
Connect the dots!
For this problem, since y
is not equal to 2x-3, the
solution cannot be on the
line
To represent this, we use
a dotted line instead of a
solid one
Graphing Systems of Inequalities
This problem also says
that y values are smaller
than 2x – 3
Let’s see what that means
Graphing Systems of Inequalities
If we plug in a value for x let’s
see what we get!
Let’s plug in 1 for x
Solve
Y is less than -1 when x is 1
Look at it on the graph
Graphing Systems of Inequalities
What values of y are less
than -1 when x is 1?
Any number below the
point (1, -1)
The same this happens
for all values of x that you
pick, y will be below the
line
Graphing Systems of Inequalities
Therefore, y will always
be below the dotted line
To show this, we shade
the graph below the
dotted line
The answer can be any
point where it’s shaded
Graphing Systems of Inequalities
Example: Find the solution of the following two
inequalities:
Since these are inequalities, we need to find the area
where they both are shaded
Graphing Systems of Inequalities
Begin with the b
Use the slope to find the
second point
Connect the dots with a
dotted line
Shade the area below the
line
Graphing Systems of Inequalities
Begin with the b
Use the slope to find the
second point
Connect the dots
This time we use a solid
line because the answer
can be on the line
Since y is less than we
have to shade below this
line also
Graphing Systems of Inequalities
The solutions to this
problem is in the green
area where both
equations are shaded.
Let’s pick a point and see
what happens
(2, -2) should make each
equation work
Graphing Systems of Inequalities
Plug in the point and see!
Since the point solves both equations it works as an
answer!
Graphing Systems of Inequalities
Look at the point again
Graphing Systems of Inequalities
1.
What’s the equation
of line a?
2.
What’s the equation
of line b?
3.
Is (2, 1) a solution?
4.
Is (-2, 1) a solution?
5.
Is (-1, 1) a solution?
a
b
Graphing Systems of Inequalities
1.
What’s the equation
of line a?
2.
What’s the equation
of line b?
3.
Is (2, 1) a solution?
4.
Is (-2, 1) a solution?
5.
Is (-1, 1) a solution?
a
b
y > x + 2
y ≤ -x
No
No
Yes
Graphing Systems of Inequalities
1.
y ≤ 3x + 2 and y < -3x + 8
2.
y > -1/2x – 1 and y ≤ 1/3x + 4
3.
y < -4x + 7 and y ≥ 2x – 5
4.
4x – 2y ≤ -2 and 6x - 3y > -9