System of Linear Inequalities
How to graph a system of linear inequalities on the coordinate plane: 3 examples and their solutions.
Example 1
Example
Solution
To graph the linear inequalities,
change the linear inequality to slope-intercept form.
Start from the first inequality x + y > 2.
The slope-intercept form is y > -x + 2.
Change 2x - y ≥ 3 to slope-intercept form.
Move 2x to the right side.
Then -y ≥ -2x + 3.
Divide both sides by -1.
Then y ≤ 2x - 3.
The divisor -1 is minus.
So the order of the inequality sign changes:
from ≥ to ≤.
Linear Inequality (One Variable)
So the given linear inequalities in slope-intercept form are
y > -x + 2 and y ≤ 2x - 3.
Let's graph these inequalities on the coordinate plane.
Graph y > -x + 2 on the coordinate plane.
Start from the y-intercept +2.
The slope is -1.
So move 1 unit to the right and 1 unit downward.
Mark the endpoint.
The inequality sign [>] doesn't include [=].
So draw a dashed line that passes through
the y-intercept +2 and the marked endpoint.
See y > -x + 2.
y is greater than the right side.
So color the upper region of the dashed line.
This is the graph of y > -x + 2.
Graph y ≤ 2x - 3 on the coordinate plane.
Start from the y-intercept -3.
The slope is 2.
So move 1 unit to the right and 2 units upward.
Mark the endpoint.
The inequality sign [≤] does include [=].
So draw a solid line that passes through
the y-intercept -3 and the marked endpoint.
See y ≤ 2x - 3.
y is less than (or equal to) the right side.
So color the lower region of the solid line.
This is the graph of y ≤ 2x - 3.
Color the intersecting region.
So the colored region is the answer.
Example 2
Example
Solution
To graph the linear inequalities,
change the linear inequality to slope-intercept form.
Start from the first inequality 2x - y > -3.
Move 2x to the right side.
Then -y > -2x - 3.
Divide both sides by -1.
Then y < 2x - 3.
The divisor -1 is minus.
So the order of the inequality sign changes:
from > to <.
Change 2x - y ≥ 1 to slope-intercept form.
Move 2x to the right side.
Then -y ≥ -2x + 1.
Divide both sides by -1.
Then y ≤ 2x - 1.
The divisor -1 is minus.
So the order of the inequality sign changes:
from ≥ to ≤.
So the given linear inequalities in slope-intercept form are
y < 2x + 3 and y ≤ 2x - 1.
Let's graph these inequalities on the coordinate plane.
Graph y < 2x + 3 on the coordinate plane.
Start from the y-intercept +3.
The slope is 2.
So move 1 unit to the right and 2 units upward.
Mark the endpoint.
The inequality sign [<] doesn't include [=].
So draw a dashed line that passes through
the y-intercept +3 and the marked endpoint.
See y < 2x + 3.
y is less than the right side.
So color the lower region of the dashed line.
This is the graph of y < 2x + 3.
Graph y ≤ 2x - 1 on the coordinate plane.
Start from the y-intercept -1.
The slope is 2.
So move 1 unit to the right and 2 units upward.
Mark the endpoint.
The inequality sign [≤] does include [=].
So draw a solid line that passes through
the y-intercept -1 and the marked endpoint.
See y ≤ 2x - 1.
y is less than (or equal to) the right side.
So color the lower region of the solid line.
This is the graph of y ≤ 2x - 1.
Color the intersecting region.
The region of y < 2x + 3 includes y ≤ 2x - 1.
So color the region of y ≤ 2x - 1.
So the colored region is the answer.
Example 3
Example
Solution
To graph the linear inequalities,
change the linear inequalities to slope-intercept form.
The slope-intercept form of 3x + y ≥ 4
is y ≥ -3x + 4.
Change 3x + y < -2 to slope-intercept form.
Then y < -3x - 2.
So the given linear inequalities in slope-intercept form are
y ≥ -3x + 4 and y < -3x - 2.
Let's graph these inequalities on the coordinate plane.
Graph y ≥ -3x + 4 on the coordinate plane.
Start from the y-intercept +4.
The slope is -3.
So move 1 unit to the right and 3 units downward.
Mark the endpoint.
The inequality sign [≥] does include [=].
So draw a solid line that passes through
the y-intercept +4 and the marked endpoint.
See y ≥ -3x + 4.
y is greater than (or equal to) the right side.
So color the upper region of the solid line.
This is the graph of y ≥ -3x + 4.
Graph y < -3x - 2 on the coordinate plane.
Start from the y-intercept -3.
The slope is -3.
So move 1 unit to the right and 3 units downward.
Mark the endpoint.
The inequality sign [<] doesn't include [=].
So draw a dashed line that passes through
the y-intercept -2 and the marked endpoint.
See y < -3x - 2.
y is less than the right side.
So color the lower region of the dashed line.
This is the graph of y < -3x - 2.
Color the intersecting region.
But there's no intersecting region.
So this system has no solution.