a. If $n$ is an integer greater than $1,$ then radical notation for $a^{1 / n}$ is ______.
b. Assume that $m$ and $n$ are positive integers that share no common factors and $n>1 .$ If $\sqrt[n]{a}$ exists, then in radical notation a^{m / n}= ______.
c. The radical notation for $x^{-1 / 2}$ is _______.
d. $8^{1 / 3}=$ _______ and $8^{-1 / 3}=$ _______..