Remember, the numerator of an exponenent represents the root. As well, a negative exponent means to take the reciprocal of the positive exponent ([tex]a^{-b} = \frac{1}{a^{b}}[/tex].
So, [tex]64^{-1/3}[/tex] is equal to [tex]\sqrt[3]{64^{-1}}[/tex] which is 1/4, because 1/4*1/4*1/4 is 1/64 (1/64 cubed root is 1/4).
For example, [tex]a^{b/c} = \sqrt[c]{b^{b}}[/tex]
The answer is c.
