📊 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 a<ba < b, then a+c<b+ca + c < b + c and ac<bca - c < b - c
  • If aba \le b, then a+cb+ca + c \le b + c and acbca - c \le b - c
  • If a>ba > b, then a+c>b+ca + c > b + c and ac>bca - c > b - c
  • If aba \ge b, then a+cb+ca + c \ge b + c and acbca - c \ge b - c
  • 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 (xx).
  • Step 2 — Apply the Inverse Operation: Perform the opposite operation on both sides of the inequality to isolate xx.
  • 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 \le or \ge), then shade the corresponding ray.
Worked Example: Solve x+83x + 8 \le 3
1. 88 is added to xx.
2. Subtract 88 from both sides: x+8838x + 8 - 8 \le 3 - 8.
3. Simplify: x5x \le -5.
4. Graph: Solid circle at 5-5, with an arrow pointing left toward -\infty.
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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 WriteType on KeyboardMath Display
Greater Than or Equal To (≥)>=
\ge
Less Than or Equal To (≤)<=
\le
Strictly Greater (>)>
>>
Strictly Less (<)<
<<
Not Equal (≠)neq
\ne
💡
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 (a<b    a±c<b±ca < b \implies a \pm c < b \pm c).
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 (\le or \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 xax \ge a), shade to the right towards positive infinity (++\infty). For x<ax < a or xax \le a, shade to the left towards negative infinity (-\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 (\ge). "At most" represents a maximum limit and translates to less than or equal to (\le).
When do you flip the inequality sign when solving an inequality?
You flip the inequality sign (e.g., from << to >>, or from \le to \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<xba < x \le b?
A compound inequality a<xba < 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 5125 \le 12), your solution and shading are probably correct (though a single test point is not a definitive proof).