๐Ÿ“Š Linear Inequalities: Two-Step Linear Inequalities

Master two-step linear inequalities: isolate variable terms, apply inverse operations, expand single parentheses, combine like terms, and check for sign flips.

Two-Step Linear Inequalities

Learning Topics

Two-Step Linear Inequalities - Solving, Distributive Property & Graphing

1. The Sequential Two-Step Strategy

To solve a two-step inequality of the form ax+b<cax + b < c (or with >>, โ‰ค\le, โ‰ฅ\ge), undo operations using inverse operations in reverse order:
  • Step 1 โ€” Isolate the Variable Term: Add or subtract constant terms from both sides to gather all constants on the opposite side.
    ax+b<cโ€…โ€ŠโŸนโ€…โ€Šax<cโˆ’bax + b < c \implies ax < c - b
  • Step 2 โ€” Isolate the Variable: Multiply or divide both sides by the coefficient of the variable. ๐Ÿšจ Golden Rule: If dividing or multiplying by a negative coefficient, remember to flip the inequality symbol!

2. Distributive Property & Combining Like Terms

Before performing the two isolation steps, simplify any complex expressions on either side:
  • Expanding Parentheses (Distributive Property): Multiply the outside term into every term inside the parentheses:
    a(x+b)โ‰คcโ€…โ€ŠโŸนโ€…โ€Šax+abโ‰คca(x + b) \le c \implies ax + ab \le c

    Example: 3(xโˆ’2)โ‰ค15โ€…โ€ŠโŸนโ€…โ€Š3xโˆ’6โ‰ค15โ€…โ€ŠโŸนโ€…โ€Š3xโ‰ค21โ€…โ€ŠโŸนโ€…โ€Šxโ‰ค73(x - 2) \le 15 \implies 3x - 6 \le 15 \implies 3x \le 21 \implies x \le 7
  • Combining Like Terms on One Side: Add or subtract the coefficients of identical variable terms before isolating:
    Example: $5x - 2x + 4 > 19 \implies 3x + 4 > 19 \implies 3x > 15 \implies x > 5$

3. Step-by-Step Solver Method

Follow this systematic 4-step framework for any two-step linear inequality:
  • Step 1 โ€” Simplify Expressions: Expand parentheses or combine like terms.
  • Step 2 โ€” Isolate the Variable Term: Add or subtract constants from both sides.
  • Step 3 โ€” Isolate the Variable: Divide or multiply by the coefficient (flip the sign if negative!).
  • Step 4 โ€” Graph & Verify: Place an open/closed circle at the boundary value, shade the solution ray, and test a point.
Worked Example: Solve โˆ’3x+7<22-3x + 7 < 22
1. Step 1 โ€” Isolate variable term: Subtract 77 from both sides:
โˆ’3x+7โˆ’7<22โˆ’7โ€…โ€ŠโŸนโ€…โ€Šโˆ’3x<15-3x + 7 - 7 < 22 - 7 \implies -3x < 15

2. Step 2 โ€” Isolate variable: Divide both sides by โˆ’3-3.
๐Ÿšจ Sign Flip: Since we divide by โˆ’3<0-3 < 0, flip << to >>:
โˆ’3xโˆ’3>15โˆ’3โ€…โ€ŠโŸนโ€…โ€Šx>โˆ’5\frac{-3x}{-3} > \frac{15}{-3} \implies x > -5

3. Graph & Solution: All real numbers strictly greater than โˆ’5-5 (open circle at โˆ’5-5, shaded right towards +โˆž+\infty).
-8-7-6-5-4-3-2-1012Test: -2
๐Ÿ’ก
๐Ÿ’ก Key Strategy: Inverse Operations & Sign Flips
Always clear addition and subtraction first before multiplying or dividing to isolate the variable. And never forget: multiplying or dividing by a negative coefficient flips the inequality sign!
Learning Topics

โ“ Frequently Asked Questions

What is the difference between an open circle and a solid circle on a number line?
An open circle (โ—‹) indicates a strict inequality (<< or >>) where the boundary point is not included. A solid circle (โ—) indicates an inclusive inequality (โ‰ค\le or โ‰ฅ\ge) where the boundary point is part of the solution.
How do I know which direction to shade on the number line?
When the variable is isolated on the left side (like x>ax > a or xโ‰ฅax \ge a), shade to the right towards positive infinity (+โˆž+\infty). For x<ax < a or xโ‰คax \le a, shade to the left towards negative infinity (โˆ’โˆž-\infty). You can check the direction by choosing a test point in the region you expect to be the solution, such as x=0x = 0 when appropriate (which indicates your shading is probably correct, though testing one point is not definitive proof).
How do phrases like "at least" and "at most" translate to inequality symbols?
"At least" represents a minimum requirement and translates to greater than or equal to (โ‰ฅ\ge). "At most" represents a maximum limit and translates to less than or equal to (โ‰ค\le).
When do you flip the inequality sign when solving an inequality?
You flip the inequality sign (e.g., from << to >>, or from โ‰ค\le to โ‰ฅ\ge) whenever you multiply or divide both sides by a negative number. Adding or subtracting numbers, or multiplying/dividing by a positive number, never flips the sign.
How do you solve and graph a compound inequality like a<xโ‰คba < x \le b?
A compound inequality a<xโ‰คba < x \le b represents the interval where xx is strictly greater than aa and at most bb. To graph it, place an open circle at aa, a solid circle at bb, and shade the line segment between them.
How can I verify if my inequality solution is correct?
Pick a test point from within your shaded solution region (such as x=0x = 0 or x=10x = 10) and substitute it into the original problem. If it yields a true statement (such as 5โ‰ค125 \le 12), your solution and shading are probably correct (though a single test point is not a definitive proof).