Question 71·Medium·Linear Inequalities in One or Two Variables
The inequality is
Which table contains only pairs that satisfy the inequality?
For inequalities with tables of points, don’t graph by hand; instead, quickly test points by substitution. Use the fact that the table must contain only satisfying points: for each answer choice, start with the first row and plug its and into the inequality—if the inequality is false, cross out the entire table immediately. Usually you can eliminate most choices with just one substitution each, then fully check the remaining table’s points, remembering that equality ( equal to the right-hand side) also counts for and .
Hints
Connect the inequality to ordered pairs
Think about what it means for a point to satisfy . What should you do with the and values from a row in the table?
Try checking just one point
Pick one point from a table, plug its and into the inequality, and see if the left side is less than or equal to the right side. Is the resulting statement true or false?
Use the word "only" to eliminate whole tables
Because each table must contain only points that satisfy the inequality, if you find even one point in a table that makes the inequality false, you can cross out that entire answer choice.
Remember the boundary line counts
The inequality is , not just . If a point makes the two sides equal, it still satisfies the inequality.
Desmos Guide
Graph the inequality
In Desmos, type y <= -1/2 x + 4. You should see a line with a shaded region below (and including) the line.
Plot the points from a table
For one answer choice, enter its three points as separate expressions, like (x1, y1), (x2, y2), (x3, y3) using the coordinates from that table. Desmos will show them as dots on the graph.
Check whether each point is in the solution region
Look to see if all three points from that table lie in the shaded region or exactly on the boundary line. If any point is above the shaded area (outside the solution region), that table cannot be correct. Repeat this for the other tables and identify which table’s three points are all inside or on the shaded region.
Step-by-step Explanation
Understand what it means for a point to satisfy the inequality
A point satisfies the inequality if, when you plug that and into the inequality, the statement you get is true.
So for any point:
- Replace with the -value from the table.
- Replace with the -value from the table.
- Check whether the left side is less than or equal to the right side.
Practice testing one ordered pair
Take a sample point, say (just to learn the process).
Substitute and into the inequality:
Compute the right side:
So we are checking , which is true. This is how you will check each point from the tables.
Eliminate tables where any point fails the inequality
Because the question says the table must contain only pairs that satisfy the inequality, if even one pair in a table makes the inequality false, that entire table is wrong.
Check each incorrect choice quickly using one point:
- Choice B, first row :
This is , which is false. So table B is out.
- Choice C, first row :
This is , which is false. So table C is out.
- Choice D, first row :
This is , which is true, so we must also check another row.
Second row of D is :
This is , which is false, so table D is also out.
Verify the remaining table fully
Now check each point in the remaining table (choice A):
- :
So is true.
- :
So is true.
- :
So is true.
All three points in this table satisfy the inequality, and we already saw every other table has at least one point that does not. Therefore, the correct answer is choice A.