📊 Linear Inequalities: One-Step Addition & Subtraction
Solve one-step linear inequalities using the addition and subtraction property of inequality, isolate variables with inverse operations, and represent solutions.
One-Step Addition & Subtraction
Learning Topics
One-Step Addition & Subtraction - Linear Inequalities
1. Addition and Subtraction Properties of Inequality
To solve an inequality, our primary goal is to isolate the variable on one side. We use the Addition and Subtraction Properties of Inequality to eliminate numbers added to or subtracted from the variable using inverse operations. Adding or subtracting the same real number from both sides produces an equivalent inequality and never changes the direction of the inequality sign:
- If , then and
- If , then and
- If , then and
- If , then and
- Why this works: It allows us to undo addition with subtraction and undo subtraction with addition, leaving the variable isolated while preserving the inequality.
2. Step-by-Step Solver Guide
To solve a one-step addition or subtraction inequality, follow these systematic steps:
- Step 1 — Identify the Operation: Determine which operation and number are affecting the variable ().
- Step 2 — Apply the Inverse Operation: Perform the opposite operation on both sides of the inequality to isolate .
- Step 3 — Simplify: Calculate the simplified result. Remember: the direction of the inequality sign remains unchanged!
- Step 4 — Graph the Solution: Mark the boundary point with an open circle (for or ) or a solid circle (for or ), then shade the corresponding ray.
Worked Example: Solve
1. is added to .
2. Subtract from both sides: .
3. Simplify: .
4. Graph: Solid circle at , with an arrow pointing left toward .
2. Subtract from both sides: .
3. Simplify: .
4. Graph: Solid circle at , with an arrow pointing left toward .
Mastering SealMath: Typing Inequality Symbols
When solving inequalities with math input, you can type inequality signs directly using simple keyboard shortcuts. The editor automatically converts them to mathematical symbols:
| To Write | Type on Keyboard | Math Display |
|---|---|---|
| Greater Than or Equal To (≥) | >= | |
| Less Than or Equal To (≤) | <= | |
| Strictly Greater (>) | > | |
| Strictly Less (<) | < | |
| Not Equal (≠) | neq |
💡
Addition and Subtraction Invariant Rule
Adding or subtracting any quantity (positive, negative, decimal, or fraction) from both sides preserves the inequality and never reverses the direction of the inequality sign ().
Learning Topics
❓ Frequently Asked Questions
What is the difference between an open circle and a solid circle on a number line?
An open circle (○) indicates a strict inequality ( or ) where the boundary point is not included. A solid circle (●) indicates an inclusive inequality ( or ) 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 or ), shade to the right towards positive infinity (). For or , shade to the left towards negative infinity (). You can check the direction by choosing a test point in the region you expect to be the solution, such as 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 (). "At most" represents a maximum limit and translates to less than or equal to ().
When do you flip the inequality sign when solving an inequality?
You flip the inequality sign (e.g., from to , or from to ) 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 compound inequality represents the interval where is strictly greater than and at most . To graph it, place an open circle at , a solid circle at , 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 or ) and substitute it into the original problem. If it yields a true statement (such as ), your solution and shading are probably correct (though a single test point is not a definitive proof).