Question 75·Hard·Linear Inequalities in One or Two Variables
Which set describes all real numbers that satisfy the inequality ?
For absolute value inequalities, immediately plan to break the problem into cases based on the sign of the expression inside the absolute value. Write one inequality assuming the inside is nonnegative and another assuming it is negative, replace the absolute value accordingly, and solve both linear inequalities carefully—especially watching for sign flips when dividing by a negative. Then remember: for (or ), the solution is usually a union of two outside intervals, while for (or ), it is usually a single middle interval, which helps you quickly check if your final answer shape makes sense.
Hints
Think about the absolute value
The inequality has . How can you rewrite an absolute value expression without the absolute value bars? Try considering when the inside, , is positive and when it is negative.
Write and solve two inequalities
Set up two cases: one with and one with . In each case, replace by either or , then solve the resulting linear inequality .
Be careful with negative coefficients
In the case where you get an inequality like , combine like terms and remember that dividing both sides by a negative number flips the direction of the inequality sign.
Combine your case results
After finding the solution from each case, think about whether you should take the intersection or the union of those solutions. For a ">" absolute value inequality, do the solutions usually form a single interval or two separate intervals?
Desmos Guide
Graph the absolute value expression
In Desmos, enter y = abs(2x - 3) to graph the absolute value function.
Graph the linear expression to compare
On a new line, enter y = x + 4. Adjust the viewing window so you can clearly see where the two graphs intersect and how they compare across the x-axis.
Use the graph to find the solution set
Click the intersection points of the two graphs and note their x-coordinates. Then look at where the graph of is above the graph of ; those x-values are the solutions to . Translate those regions on the x-axis into interval notation or inequalities.
Step-by-step Explanation
Set up cases for the absolute value
The expression depends on the sign of .
- If , then .
- If , then .
So we will solve the inequality in two cases:
- .
Case 1: When
First find when :
In this case, , so the inequality becomes
Solve it:
In Case 1, we also need . Since every already satisfies , the solution for this case is
- .
Case 2: When
Now find when :
In this case, , so the inequality becomes
Solve it carefully (watch the sign when dividing by a negative):
In Case 2, we also need . Every is already less than , so the solution for this case is
- .
Combine both case results
From Case 1, we got . From Case 2, we got .
Because holds in either case, we take the union of these two solution sets:
- All real numbers less than , or
- All real numbers greater than .
So the solution set is or , which corresponds to answer choice A.