Question 51·Hard·Linear Inequalities in One or Two Variables
The system of inequalities is
Which point lies in the region defined by the system?
For systems of inequalities with a small set of answer choices, it is fastest to test each point directly instead of fully graphing. Plug the and values from each choice into one inequality at a time, eliminating any point that fails even one inequality. Pay special attention to strict inequalities ( or ): if substitution makes both sides equal, the inequality is not satisfied. Continue until only one point satisfies all given inequalities.
Hints
Think about what it means to be in the region
A point lies in the region defined by a system of inequalities only if it makes every inequality in the system true. If one inequality fails, that point is not in the region.
Use substitution instead of graphing
Rather than graphing, try plugging the and values from each answer choice into the inequalities to see which choices satisfy all of them.
Eliminate choices step by step
Start with one inequality (for example, ) and test all four points. Cross out any that fail. Then test the remaining points in the next inequality, and so on, until only one point remains.
Pay attention to strict vs. non-strict inequalities
Notice that one inequality uses (strictly less than), not . A point that makes the two sides equal does not satisfy a strict inequality.
Desmos Guide
Graph the inequalities
In Desmos, enter each inequality on its own line:
3x - 2y <= 12x + y >= 4y < 2x - 1Make sure the regions are shaded, and notice that the boundary is shown as a dashed line, meaning points on that line are not included.
Plot the answer-choice points
On separate lines, type each point exactly as written: (6, 0), (4, 1), (2, 3), (5, -1). Desmos will show each as a dot on the graph.
Identify which point lies in the intersection region
Look at the overlapping shaded region where all three inequalities are satisfied. Check which of the plotted points lies inside this overlapping shading and is not on the dashed boundary line of the strict inequality. The coordinates of that point correspond to the correct answer choice.
Step-by-step Explanation
Understand what the system means
The three inequalities
define three half-planes on the coordinate plane. A point lies in the region defined by the system only if it makes every inequality true at the same time. If a point fails even one inequality, it is not in the region.
Test each point in the first inequality
Use .
- For : , and is false, so is rejected.
- For : , and is true.
- For : , and is true.
- For : , and is false, so is rejected.
After this step, only and are still possible.
Test remaining points in the second inequality
Now use .
- For : , and is true.
- For : , and is true.
Both remaining points still work for the first two inequalities, so we must use the third inequality to decide between them.
Use the strict inequality to decide
The last inequality is strict: . Equality is not allowed.
- For : . We get , which is true.
- For : . We get , which is false because is equal to , not less than.
So only satisfies all three inequalities. The correct answer is .