Question 116·Medium·Linear Inequalities in One or Two Variables
The inequality is
For which table are all the listed pairs solutions of the inequality?
For inequalities of the form , the fastest approach is substitution and elimination: for each answer choice, plug the x-value of a point into , compute the result, and immediately compare it to the y-value. As soon as you find a point where is greater than , cross off that entire choice and move on. You rarely need to check all four tables in full; often, checking just the first point or two in each is enough to isolate the one table where every point satisfies the inequality (including cases where equals ).
Hints
Connect each ordered pair to the inequality
Remember that to check if a point is a solution to an inequality like , you substitute the x-value into the expression and compare the result with the y-value.
Check one point at a time
Pick one answer choice and test its first point: compute for that x-value and see whether the inequality (that result) is true. If it fails for even one point, that entire answer choice cannot be correct.
Look for equality as well as "less than"
Because the inequality is , points where is exactly equal to do count as solutions. Do not discard points just because equals instead of being smaller.
Eliminate quickly
You do not need to check every point in a table if you already find one that does not satisfy the inequality—cross off that choice and move on to the next.
Desmos Guide
Graph the inequality
In Desmos, type y <= -3x + 7. You should see the line with shading on one side—this shaded region (including the line itself) represents all solutions to the inequality.
Plot the points from one answer choice
For a chosen table, enter each point as its own expression, such as (2,2), (1,5), (0,8) for option A. Desmos will display these as dots on the graph.
Check whether the points are in the solution region
Look to see if each dot lies either exactly on the line or inside the shaded region. If any point is outside the shaded area (above the line), that answer choice is not correct. Repeat this process with the other tables until you find a table where all its points lie in the shaded region or on the boundary line; that table’s pairs are all solutions to the inequality.
Step-by-step Explanation
Understand what it means to be a solution
An ordered pair is a solution to the inequality if, when you plug the x-value into , the resulting value is greater than or equal to the given y-value.
In other words, for each point, compute and check whether .
Test the pairs in option A
Option A has points , , and .
- For :
.
Check: Is ? No. So is not a solution.
Since even one point in the table is not a solution, the entire table for option A cannot be correct.
Test the pairs in options B and D
Option B has , , and .
- For :
.
Check: Is ? No. So option B is eliminated.
Option D has , , and .
- For :
.
Check: Is ? No. So option D is also eliminated.
So far, none of these tables have all their points satisfying the inequality.
Test the remaining table (option C)
Option C has , , and .
- For :
.
Check: Is ? Yes. - For :
.
Check: Is ? Yes. - For :
.
Check: Is ? Yes.
All three ordered pairs in this table satisfy , so choice C is the correct answer.