Bounded Subset of Real Numbers/Examples

Examples of Bounded Subsets of Real Numbers

Example 1

The subset $S$ of the real numbers $\R$ defined as:

$S = \set {1, 2, 3}$

is bounded both above and below.

Some upper bounds of $S$ are:

$100, 10, 4, 3$

Some lower bounds of $S$ are:

$-27, 0, 1$

Example 2

The subset $T$ of the real numbers $\R$ defined as:

$T = \set {x \in \R: 1 \le x \le 2}$

is bounded both above and below.

Some upper bounds of $T$ are:

$100, 10, 4, 2$

Some lower bounds of $T$ are:

$-27, 0, 1$

Reciprocals of Positive Integers

The subset $T$ of the real numbers $\R$ defined as:

$T = \set {\dfrac 1 n: n \in \Z_{>0} }$

is bounded both above and below.

We have that:

$\sup T = 1$

$\inf T = 0$

where $\sup T$ and $\inf T$ denote the supremum and infimum of $T$ respectively.

We also have:

$\sup T \in T$

$\inf T \notin T$