What is an expression for 9

There are millions of them ... an infinite number of them, I think.

Here are a few of them:

9 x 1

(3) ²

(-3) ²

(4 + 5)

3 x 3

(8 + 1)

√81

(11 - 2)

(-√3) ⁴

7 sin (90°) - 2 cos (180°)

(27 seconds) / (3 Hz)

(999 - 990)