Not quite ggx. Think about square root, cube root, fourth root, fifth root, etc of a number (X) as that number (X) raised to a power of 1/2 (0.5), 1/3 (~0.33), 1/4 (0.25), 1/5 (0.2), etc respectively. So for example, the fifth root of X would be, X^1/5. But, to put that argument into action, you'll want to write it like so:

and this should give you the cube root of the number X, while this:

will give you the fifth root of X. Where X is a double. Gosh! I hope you understand. To learn more of these, google 'Indices and logarithms'.