Fractional Exponents-Section 4.3
Working with fractional exponents.
For a video explanation see
https://www.khanacademy.org/math/arithmetic/exponents-radicals/negative-exponents-tutorial/v/zero--negative--and-fractional-exponents
or http://patrickjmt.com/evaluating-numbers-raised-to-fractional-exponents/
or http://patrickjmt.com/exponents-evaluating-numbers-raised-to-fractional-exponents/
or http://patrickjmt.com/exponents-evaluating-numbers-with-rational-exponents-by-using-radical-notation-basic-ex-1/