A rational number is any number that can be expressed as a fraction (p)/(q), where p and q are integers and q != 0.

Here's how to show that the given numbers are rational by expressing them as fractions:

A rational number is any number that can be expressed as a fraction $\frac{p}{q}$, where $p$ and $q$ are integers and $q \neq 0$.

Example given in the image:
$2.1^\cdot$
Let $x = 2.111...$ (1)
Multiply by 10 to shift the repeating digit:
$10x = 21.111...$ (2)
Subtract (1) from (2):
$10x - x = 21.111... - 2.111...$
$9x = 19$