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Interval Notation Calculator

Enter your inequality to see the correct interval notations with step-by-step explanation.

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Interval Notation Calculator

This Interval Notation Calculator helps you convert mathematical inequalities into proper interval notation easily. Whether you're a student learning algebra, a teacher explaining number systems, or a math enthusiast, this tool allows you to represent solution sets and numerical ranges accurately. It clearly explains the meaning of every bracket, parenthesis, and infinity symbol, helping you avoid mistakes and understand interval notation better.

What is Interval Notation?

Interval notation is a mathematical method used to describe a continuous range of numbers on a number line. Instead of writing inequalities in long form, interval notation offers a compact and readable format.

For example, the inequality 2 ≤ x < 5 can be written as [2, 5). The symbols indicate whether endpoints are included or excluded:

  • [ ] – Square brackets indicate that the endpoint is included (closed interval)
  • ( ) – Parentheses indicate that the endpoint is excluded (open interval)
  • – Infinity always uses parentheses because it does not represent a specific number

Interval notation is commonly used to describe domains, ranges, and solution sets in algebra and calculus, simplifying real number set representation and improving readability.

Why Use Interval Notation?

Interval notation provides a concise way to represent inequalities and continuous numerical ranges. It is especially helpful for:

  • Expressing domains and ranges of functions
  • Writing solutions of linear and compound inequalities
  • Illustrating intervals on a number line

Using an interval notation calculator reduces errors and saves time, particularly when working with infinity or multiple inequalities.

How to Find the Interval Notation

Let’s go through an example to convert an inequality into interval notation.

Example:

Convert the inequality 7 - x/6 > 8 into interval notation:

Step 1: Isolate the variable

7 - x 6 > 8

Subtract 7 from both sides:

- x 6 > 1

Step 2: Remove the negative sign

Multiply both sides by -1 and reverse the inequality sign:

x 6 < -1

Step 3: Clear the denominator

Multiply both sides by 6:

x < -6

Step 4: Write in interval notation

Since x is less than -6, the interval notation is:

(-∞, -6)

Result Interpretation:

  • Parentheses are used because -6 is not included in the solution.
  • The infinity symbol always uses parentheses since it represents an unbounded value.

Types of Intervals

Intervals are classified based on whether their endpoints are included or excluded:

1. Open Interval

An open interval does not include its endpoints. For example, {x | 2 < x < 5} is written as (2, 5).

Open interval image

2. Closed Interval

A closed interval includes both endpoints. For example, {x | 2 ≤ x ≤ 5} is written as [2, 5].

Closed interval image

3. Half-Open Interval

A half-open interval includes one endpoint and excludes the other. For example, {x | 2 ≤ x < 5} is written as [2, 5).

Half open interval image

Interval Notation for All Real Numbers

The interval notation representing all real numbers is:

(-∞, ∞)

References

Wikipedia: Interval (Mathematics)

Brilliant: Writing Interval Notation

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