Interval Representation

Rarely Tested

Interval Representation

## Definition / Concept

Intervals represent subsets of the real numbers using endpoint conditions.

## Formula

$$[a,b]=\{x\in\mathbb R:a\le x\le b\}$$

$$[a,b)=\{x\in\mathbb R:a\le x<b\}$$

$$(a,b]=\{x\in\mathbb R:a<x\le b\}$$

$$(a,b)=\{x\in\mathbb R:a<x<b\}$$

## Terminologies

- Closed interval → Both endpoints are included.

- Open interval → Neither endpoint is included.

- Half-open interval → Exactly one endpoint is included.

## Conditions / Special Cases

$$(-\infty,a)=\{x\in\mathbb R:x<a\}$$

$$(-\infty,a]=\{x\in\mathbb R:x\le a\}$$

$$[a,\infty)=\{x\in\mathbb R:x\ge a\}$$

$$(a,\infty)=\{x\in\mathbb R:x>a\}$$

## Usage

- Used to express domains, ranges and solution sets of inequalities.

Question 1

The number of the real solutions of the equation:
$$x|x+3|+|x-1|-2=0$$ is

Question 2

Let $$[x]$$ denote the greatest integer less than or equal to $$x$$. Then, the values of $$x \in R$$ satisfying the equation $$[e^x]^2 + [e^x + 1] - 3 = 0$$ lie in the interval:

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