Answer
True
Work Step by Step
A rational number is a number that can be expressed as a quotient of two integers.
Note that $9 = \frac{18}{2}$.
18 and 2 are integers.
Thus, $9$ is a rational number.
$\in$ means that the number is an element of the given set.
Since $9$ is a rational number, it is an element of the set of rational numbers.
Therefore, the given statement is true.
