Can you explain me 9** (1/2)

Answer 1

It's more of maths than programming.

M raised to power of 1/n is equal to nth root of M.

So 9**(1/2) is square root of 9.

Answer 2

A little more detail: ** is the power operator in python and at least newest versions of js...

In mathematical expressions, we have more commonly the habits to see the ^ sign for the power operator:

(math context) x ^ y
is equivalent to:
(code context) x ** y

... and should be pronounced "x raised to the power of y"