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 (−∞, ∞).