Question 99·Hard·Linear Inequalities in One or Two Variables
Consider the system of inequalities
Which of the following tables lists ordered pairs that all satisfy both inequalities?
For systems of inequalities with answer choices given as points or tables, the fastest approach is usually to plug in: for each table, pick a point and substitute its coordinates into each inequality, looking for a quick contradiction. Use the inequality signs carefully—pay special attention to whether the boundary is strict (>, <) or inclusive (≥, ≤), because many trap answers place a point exactly on a line that is not included. As soon as you find a point in a table that fails even one inequality, cross off that entire choice and move on; you often do not need to test every point in every table.
Hints
Remember what it means to satisfy a system
A point satisfies a system of inequalities only if it makes every inequality in the system true at the same time.
Substitute the coordinates
Pick a point from any table, substitute its and values into each inequality, and see whether each statement is true or false.
Watch the inequality symbols closely
In the first inequality, , equality is not allowed; in the second, , equality is allowed. Check carefully when equals the expression on the right.
Eliminate rather than confirm
Look for a point in each table that fails at least one inequality—if you find even one, you can cross off that entire answer choice.
Desmos Guide
Graph the boundary lines and inequalities
In Desmos, enter y > 0.5x - 3 and y <= -x + 4. Desmos will shade the region for each inequality; the solution set to the system is the overlapping shaded region.
Plot the answer choice points as separate points
For each table, enter its points as separate expressions, for example: (−2,−1), (4,2), (0,1) for one table. Do this for each answer choice (you can label them A, B, C, D in Desmos if you like).
See which table’s points all lie in the overlap
Look at where each point falls relative to the overlapping shaded region. The correct answer is the table whose three points all lie inside (or, when allowed, on the boundary of) the overlapping region, with none lying outside it.
Step-by-step Explanation
Understand what it means to satisfy a system of inequalities
We have the system
For a point to satisfy this system:
- It must make both statements true at the same time.
- The first inequality is strict: must be greater than, not equal to, .
- The second inequality allows equality: can be less than or equal to .
Practice checking one point
To check a point, replace and in each inequality.
Example: test .
- First inequality: plug in , .
- Compute .
- Check , which is true.
- Second inequality: plug in , .
- Compute .
- Check , which is true.
So satisfies both inequalities. You will repeat this process for each point in each table.
Eliminate tables that contain a point that fails
Now test points from the answer tables, looking for a single point that violates either inequality.
-
Table with :
- We already saw works.
- Check in the second inequality: .
- Compute .
- Check , which is false, so does not satisfy the system.
- Therefore this table cannot be correct.
-
Table with :
- Check in the first inequality: .
- We found .
- Check , which is false (it is equal, not greater).
- So fails the first inequality, and this table cannot be correct.
- Check in the first inequality: .
-
Table with :
- Check in the first inequality.
- Compute .
- Check , which is false (again, equal, not greater).
- So fails the first inequality, and this table cannot be correct.
- Check in the first inequality.
The remaining table (the only one we have not ruled out) must have all its points satisfying both inequalities.
Confirm the remaining table is correct
The remaining option lists the pairs , , and .
- We already checked and saw it works.
- Check :
- First inequality: , and (true).
- Second inequality: , and (true).
- Check :
- First inequality: , and (true).
- Second inequality: , and (true).
All three points in this table satisfy both inequalities, so the correct answer is the table of pairs .