Lesson 3 of 8
Inequalities & The Flip Rule
Inequalities use the signs less-than, greater-than, less-than-or-equal, and greater-than-or-equal instead of an equals sign. You solve them almost exactly like equations, doing the same thing to both sides.
REMEMBER
If you multiply or divide both sides by a NEGATIVE number, flip the inequality sign. Less-than becomes greater-than, and so on. This is the one rule everyone forgets.
- 1Solve -2x + 1 less-than 9
- 2Subtract 1 from both sides: -2x less-than 8
- 3Divide both sides by -2 AND flip the sign: x greater-than -4
Graphing on a number line
- ●Use an OPEN circle for less-than or greater-than (the number is not included)
- ●Use a CLOSED (filled) circle for less-than-or-equal or greater-than-or-equal (the number is included)
- ●Shade toward the numbers that make it true: right for greater-than, left for less-than
ON THE TEST
Open circle means the dot is hollow, the endpoint is not part of the answer. Filled circle means it counts.