Solving Multi-Step Inequalities
Introduction
Multi-step inequalities extend the ideas from one-step inequalities by adding layers: combining like terms, distributing, and sometimes dealing with negative coefficients.
Because inequalities describe ranges of solutions rather than single values, each step must preserve the direction of the inequality — except when multiplying or dividing by a negative number, which flips the inequality sign.
This article assumes you already understand:
- How to isolate a variable in a one-step inequality
- How to add, subtract, multiply, or divide both sides of an inequality
- The meaning of inequality symbols ($<, >, \le, \ge$)
What Are Multi-Step Inequalities?
A multi-step inequality is any inequality that requires more than one algebraic operation to isolate the variable.
Examples:
- $3x - 7 \le 11$
- $4 - 2(x + 3) > 10$
- $5x + 8 \ge 3x - 4$
Typical steps include:
- Combining like terms
- Using the distributive property
- Moving variable terms to one side
- Handling negative coefficients carefully
Key Idea: Flipping the Inequality
When solving inequalities, the only time the inequality sign flips is when you:
- Multiply both sides by a negative number
- Divide both sides by a negative number
Examples:
- If $-2x > 6$, dividing by $-2$ gives $x < -3$
- If $-5y \le 20$, dividing by $-5$ gives $y \ge -4$
This rule is essential for solving inequalities with negative coefficients.
General Strategy for Solving Multi-Step Inequalities
- 1. Distribute
Apply the distributive property if parentheses are present. - 2. Combine like terms
Simplify each side of the inequality. - 3. Move variable terms to one side
Use addition or subtraction to gather all $x$-terms on one side. - 4. Isolate the variable
Multiply or divide to solve for the variable.
Flip the sign if dividing/multiplying by a negative. - 5. Represent the solution
- As an inequality
- On a number line
- In interval notation (optional)
Worked Examples
Example 1
Solve: $$3x - 5 \ge 7$$ Steps:
- Add $5$ to both sides: $3x \ge 12$
- Divide by $3$: $x \ge 4$
Example 2
Solve: $$4 - 2(x + 1) < 6$$ Steps:
- Distribute: $4 - 2x - 2 < 6$
- Combine like terms: $2 - 2x < 6$
- Subtract $2$: $-2x < 4$
- Divide by $-2$ and flip the sign: $x > -2$
Example 3
Solve: $$5x + 8 \le 3x - 4$$ Steps:
- Subtract $3x$: $2x + 8 \le -4$
- Subtract $8$: $2x \le -12$
- Divide by $2$: $x \le -6$
Calculator
Solving inequalities
- As with one-step inequalities, multi-step inequalities can be solved via the $\operatorname{solveLinearInequality}()$ function
- Note that the inequality must be wrapped in quotes to stop the calculator evaluating it first
solveLinearInequality('3 - 2(x - 4) <= 11') solveLinearInequality('7 - (x + 2) > 3x')
Exercises
- Solve the inequality: $4x - 7 > 9$
- Solve: $3 - 2(x - 4) \le 11$
- Solve: $5x + 12 \ge 2x - 6$
- Solve the inequality with a negative coefficient: $-3x + 5 < 2$
- Solve: $7 - (x + 2) > 3x$
- Solve: $-4(2x - 1) \ge 12$
- Solve: $2x + 3 < 5x - 9$
- Solve the inequality and remember to flip the sign: $-5(x - 2) \le 15$