Algebra 1 / Unit 3: Solving Inequalities
3.3 Compound Inequalities
Notes
A compound inequality joins two inequalities.
- And: both must be true. $-2 < x \le 4$ is the overlap between $-2$ and 4.
- Or: at least one must be true. $x < -1$ or $x > 3$ shades two separate pieces.
- Solve "and" inequalities by doing the same thing to all three parts: $-3 \le 2x + 1 < 7 \Rightarrow -4 \le 2x < 6 \Rightarrow -2 \le x < 3$.
Practice
Solve $-1 < x - 4 < 6$.
Add 4 to all three parts.
Which number satisfies $x \le -2$ or $x > 5$?
7 is greater than 5.
Solve $\displaystyle 1 \le \frac{x}{2} + 3 \le 5$.
Subtract 3: $\displaystyle -2 \le \frac{x}{2} \le 2$. Multiply by 2.
Ready for more? Take the Unit 3 test.