Question 107·Medium·Linear Inequalities in One or Two Variables
Consider the system of inequalities in the -plane:
Which point is in the solution set?
For SAT questions asking which point satisfies a system of inequalities, it’s usually fastest to plug each answer choice into the inequalities instead of graphing. Substitute the x- and y-values into the first inequality and quickly decide if it’s true; eliminate any point that fails. Then test the remaining points in the second inequality, paying close attention to whether the inequality is strict ( or ) or inclusive ( or ). This systematic elimination reduces errors and saves time.
Hints
Think about what a solution to a system means
A solution to a system of inequalities must make every inequality true at the same time. If a point fails even one inequality, it is not in the solution set.
Substitute coordinates into the first inequality
Take each answer choice and plug and into . Decide if the statement is true or false for each point.
Use the second inequality to narrow it down
For any point that works in the first inequality, substitute into . Be careful with the direction of the inequality sign and remember that does not allow equality.
Eliminate choices systematically
Cross out any point that fails one of the inequalities. The remaining point (if you checked carefully) will be the one in the solution set.
Desmos Guide
Graph the first inequality
In Desmos, enter y >= 2x - 3. You should see the line with the region above and on the line shaded.
Graph the second inequality
Enter y < x + 1. This will show the line with the region below but not on that line shaded.
Find the overlapping region
Look for the part of the plane where the two shaded regions overlap. That overlapping region represents all points that satisfy both inequalities.
Check the answer choices
Type each answer choice as a point in Desmos, like (2, 0), (1, -1), (0, 2), and (3, 5). See which point lies inside the overlapping shaded region; that point is in the solution set.
Step-by-step Explanation
Understand what the solution set means
A point is in the solution set of a system of inequalities only if it makes every inequality in the system true when you substitute and into each one. Here, each answer choice is a point; we just need to test them one by one.
Test each point in the first inequality
The first inequality is .
For each point, plug in its and values:
- For : check if .
- For : check if .
- For : check if .
- For : check if .
Decide for each point whether this inequality is true or false. Any point that makes this false cannot be in the solution set.
Test each remaining point in the second inequality
Now use the second inequality: .
For any point that passed the first inequality, plug into this one:
- Use its and values and check if is true.
Remember: the symbol means strictly less than, so if equals , it does not satisfy this inequality.
Find the point that satisfies both inequalities
Compare your results:
- Some points fail the first inequality and are eliminated.
- Among the points that satisfy the first inequality, check which also satisfy .
The only point that makes both inequalities true is , so is in the solution set.