Question 137·Medium·Linear Inequalities in One or Two Variables
For which of the following tables are all the listed pairs solutions to the inequality above?
For inequality-with-table questions, translate “solution” into “plug in and check.” Quickly substitute each pair from a table into the left side of the inequality, compute , and compare the result to the boundary value (here, ). Eliminate any table as soon as you find one pair that makes the inequality false, and look for the single table where every listed pair makes the inequality true; this substitution-and-elimination process is fast and reliable under timed conditions.
Hints
What does the inequality ask for?
Think about what it means for an pair to satisfy . What should happen when you plug in those values?
Use substitution for each pair
For each row in a table, replace with the -value and with the -value in . Then compare the result to .
Eliminate tables efficiently
You do not need to check every single pair if you already find one that does not satisfy the inequality in that table. As soon as is less than for a pair, you can cross out that whole table.
Look for values clearly too small
Watch for pairs where both and are small or where is negative—these are more likely to make less than and help you eliminate a table quickly.
Desmos Guide
Check the inequality expression for each pair
For any table you want to test, type an expression in Desmos for each row using its - and -values, like 5*(x-value) + 2*(y-value) (for example, 5*4+2*3).
Compare each result to 26
Look at Desmos’s output for each expression. If every row in that table gives an output that is , then all its pairs satisfy the inequality. If any row gives a result less than , that table is not the answer.
Step-by-step Explanation
Understand what it means to be a solution
The inequality is . An pair is a solution if, when you plug the and values into , the result is greater than or equal to .
Test a single ordered pair
Pick one ordered pair and substitute it into .
Example: For ,
Since , this pair does satisfy the inequality. You will do this kind of check for each pair in a table.
Check each table for a failing pair
For each answer choice (each table):
- Take the first row, plug into , and see if the result is at least .
- If it is, move to the next row in that same table and repeat.
- If any row in a table gives a result less than , that entire table cannot be correct.
You only need one failing pair to eliminate a table.
Compare the tables and identify the only one with all solutions
Work through the rows:
- In one table, all three pairs give values or greater when plugged into , so every pair is a solution.
- In each of the other tables, at least one pair gives a value less than , so those tables include non-solutions.
Therefore, the correct table is the one with the pairs , , and .