Fractional exponents are abbreviations for taking the roots of a number. For example, x½ means 
, the square root of x. This makes sense because, by the rules of addition for exponents:
(x½)(x½) = x(½ + ½) = x1 = x
In the same way, x⅓ is the cube root of x. We need to multiply x⅓ by itself three times to get back to x. Moving along, x¼ is the fourth root of x, x⅕ is the fifth root of x, and so on. What's that? You want one more? All right, all right: x⅙ is the sixth root of x, but that's all you're getting from us.
What about fractions that have a number other than 1 in the numerator? Can we ignore them and move on to easier problems? Unfortunately, no. That big gaping hole on your answer sheet will be glaring. What would x¾ mean? Well, if we multiply x¾ by itself 4 times, we get x3. Therefore, x¾ is still a root; it's the fourth root of x cubed. By the rules of multiplying exponents, we can also write x¾ as (x3)¼, or as (x¼)3.
We could write it many other ways as well, but those other ways would be wrong, and if simplifying an exponent is wrong, we don't want to be right. Wait, what?
Sample Problems
The expression 8⅔ can also be written as (8⅓)2 . Since the cube root of 8 is 2, this simplifies to (2)2 = 4.
The expression 
can be written as 
which simplifies to 
.