Question 36·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 SAT questions that give a system of inequalities and a short list of candidate points (often arranged in tables), the fastest method is usually direct substitution rather than graphing. For each table, plug each point into both inequalities and check whether the resulting statements are true; eliminate any table as soon as you find a point that fails even one inequality. Pay close attention to inequality symbols (, , , ) and signs when computing, and remember that every point in the correct table must satisfy all inequalities in the system.
Hints
Think about what it means to satisfy an inequality
For an ordered pair , you "test" it by substituting the and values into the inequality and checking whether the resulting statement is true.
Apply the test to each table
Pick one ordered pair from a table, substitute it into both inequalities, and see if both are true. If even one inequality is false for that pair, the whole table cannot be correct.
Be efficient
You do not need to test all three points if you already find one that fails; as soon as any point in a table does not satisfy both inequalities, you can eliminate that table.
Watch the inequality symbols
Pay close attention to versus ; a value that is equal to 3 does not satisfy , and a value greater than 10 does not satisfy .
Desmos Guide
Graph the system of inequalities
In Desmos, enter the inequalities as y >= 4x - 10 and y > (3 - x)/2. You should see two shaded regions; the solution set is where the two shaded regions overlap.
Enter points from a table
For a given answer option, type each ordered pair as a point, for example (4,8), (1,-2), (0,4), and so on. Desmos will plot these as dots on the graph.
Check which table’s points lie in the solution region
For each table, see whether all three plotted points lie in the overlapping shaded region that represents the system’s solutions. The correct table is the one whose three points all fall inside that overlapping region.
Step-by-step Explanation
Understand what the question is asking
The system is
An ordered pair satisfies the system only if both inequalities are true after you plug in that and . A table is correct only if all three of its ordered pairs make both inequalities true.
Rewrite the inequalities (optional but helpful)
You can solve each inequality for to better see what is going on.
From :
From :
So any solution must have and . In practice, though, for a question with a short list of points, it is usually fastest just to substitute each pair into the original inequalities.
Test the ordered pairs in options A and B
Use the original inequalities and substitute.
Option A: (4,8), (1,-2), (0,4)
- :
- ✔
- ✔
- :
- ✔
- ✘ (this is false)
Since does not satisfy the second inequality, Option A is not correct.
Option B: (3,6), (5,12), (-1,-4)
- :
- ✔
- ✔
- :
- ✔
- ✔
- :
- ✔
- ✘ (this is false)
Because fails the second inequality, Option B is also not correct.
Test the ordered pairs in options C and D and decide
Option C: (2,2), (0,5), (3,7)
- :
- ✔
- ✔
- :
- ✔
- ✔
- :
- ✔
- ✔
All three ordered pairs in Option C satisfy both inequalities.
Option D: (-2,0), (4,6), (2,1)
- :
- ✔
- ✘ (false)
Since does not satisfy the second inequality, Option D is not correct.
Therefore, the only table in which all ordered pairs satisfy both inequalities is Option C: Table of pairs (2,2), (0,5), (3,7).