Activity
For questions 1 – 5, use the following scenario to graph an inequality from a table:
Andre is making trail mix with dried fruit and mixed nuts. Dried fruit costs $3 per pound and mixed nuts cost $6 per pound. He wants to spend no more than $54 on the trail mix. The inequality represents the number of pounds of dried fruit, , he can buy for pounds of nuts.
The related equation represents the boundary line of the inequality. Complete the table of values to find points on the boundary line of the inequality.
0 | |
2 | |
4 | |
6 |
Compare your answer:
0 | 18 |
2 | 14 |
4 | 10 |
6 | 6 |
Use the graphing tool or technology outside the course. Graph the data from your table of values that represents this scenario using the Desmos tool below.
Compare your answer:
Is the boundary line for the inequality a solid line or a dashed line? Explain how you know.
Compare your answer:
The line is solid because the inequality means the points on the line are included as solutions.
Is the point a solution to the inequality?
Compare your answer:
Yes, , .
Use the graph from number 2. Enter the inequality to represent the data. Notice the shading for the solution region of this inequality.
Compare your answer:
In problems 6–10, use the data from the table to graph the inequality and write an inequality with two variables.
-2 | -5 |
0 | -6 |
2 | 1 |
3 | 5 |
Use the graphing tool or technology outside the course. Graph the data from your table of values that represents this scenario using the Desmos tool below.
Compare your answer:
Now, in the Desmos window graph .
Compare your answer:
How does the line need to move to capture all of the points?
Compare your answer:
Answers may vary.
Increase the y-intercept or the slope to capture the point .
Using desmos, adjust the slope and/or the -intercept to find an inequality that could be a possibility.
Compare your answer:
Answers may vary.
These are possible representation of where the line could on the graph
Less than
Less than or equal to
Greater than
Greater than or equal to
Not a solution
Use the graph from number 7. Shade the correct side of the boundary line to represent the inequality .
Compare your answer:
Self Check
Which table of values can be used to graph the boundary line of the inequality ?
Additional Resources
Connecting Representations of Inequalities
Tables can be used to help you to write and solve inequalities in two variables.
Part 1: Writing Inequalities in Two Variables Given A Set of Data in a Table
Write a linear inequality in two variables based on the given data:
-4 | -3 |
-2 | -2 |
0 | -1 |
2 | 0 |
Remember that for an inequality the points could be on the line, above the the line, or below the line. The type of inequality will differ based on these conditions.
On the line | or |
Above the line | |
Below the line |
If you are given a set of possible points like the table above, there could be multiple lines that the data points could represent. Let’s figure out a few possibilities for this given set.
Step 1 - Graph the points on a coordinate plane.
Step 2 - Determine possible lines.
Remember that the dots can be on the line, but they all have to be either above or below to create an inequality. If the line has points on both sides, then the line isn’t a possibility.
Let’s try a few possibilities. We can start with the equation to see if the points are above the line or below the line.
The equation cannot be a possibility because there are points above and below the line.
Step 3 - Adjust the slope or -intercept
We can change the slope and the y-intercept to see how we can shift the line to be able to capture all the points. Let’s move the line to below the and . We can leave the slope as 1 and change the y-intercept to -7.
There is still one point below the line. We could decrease the slope of the line to .
Now all of the points are above the line. This means that the value of is always greater than the value.
So, one of the possible solutions could be .
Part 2: Using Tables to Solve Inequalities in Two Variables
Graph the linear inequality using a table.
Step 1 - Create a table of values using the related equation to identify points on the boundary line of the inequality.
−4 | −3 |
−2 | −2 |
0 | -1 |
2 | 0 |
Step 2 - Plot the points and sketch the boundary line.
If the inequality is or , the boundary line is solid.
If the inequality is or , the boundary line is dashed.
The inequality sign is , so we draw a dashed line.
Step 3 - Test a point that is not on the boundary line. Is it a solution of the inequality?
Test as it is not on the boundary line of the inequality.
is False.
So, is not a solution.
Step 4 - Shade in one side of the boundary line.
If the test point is a solution, shade in the side that includes the point.
If the test point is not a solution, shade in the opposite side.
The test point is not a solution, so shade in the side of the boundary line that does not include .
All points in the shaded region and not on the boundary line represent the solutions to .
Try it
Try It: Graph Linear Inequalities in Two Variables
Is the inequality a solution for the table of values? Explain your reasoning.
-4 | -3 |
-2 | -2 |
0 | -1 |
2 | 0 |
Compare your answer:
No, the point sits on the line so it can’t be greater than or less than.
Use a table to graph the inequality .
Compare your answer:
Here’s how to solve an inequality using a table:
Step 1 - Create a table of values using the related equation to identify points on the boundary line of the inequality.
x | y |
---|---|
−4 | −5 |
−2 | −1 |
0 | 3 |
2 | 7 |
Step 2 - Plot the points and sketch the boundary line.
If the inequality is or , the boundary line is solid.
If the inequality is or , the boundary line is dashed.
The inequality sign is , so we draw a solid line.
Step 3 - Test a point that is not on the boundary line. Is it a solution of the inequality?
Test as it is not on the boundary line of the inequality.
is True.
So, (0, 0) is a solution.
Step 4 - Shade in one side of the boundary line.
If the test point is a solution, shade in the side that includes the point.
If the test point is not a solution, shade in the opposite side.
The test point is a solution, so shade in the side of the boundary line that includes .
All points in the shaded region and not on the boundary line represent the solutions to .