You may want to review roots and domains first.

Remember that a number might not have a given kind of root. In
particular, if a number is negative, it doesn't have any square
roots, or fourth roots, of sixth roots, or roots of any even
order. (The number before the “th” is called
the *order* of the root.) So to find the domain
of ^{6}√((−3 ⁄ 8)*x*
− 1 ⁄ 12), say, you have to solve
(−3 ⁄ 8)*x* −
1 ⁄ 12 ≥ 0. (Recall that the domain is the
set of values of *x* for which it makes sense.) The solution
is the interval (−∞,
−2 ⁄ 9], so that's the domain.

If the order is odd, then the root always exists. So the domain
of ^{5}√((−3 ⁄ 8)*x*
− 1 ⁄ 12) is all numbers, which we can
write as (−∞, ∞).