The given expression is:
[tex] \sqrt[3]{ 8^{x} } [/tex]
Verbally we can say we are taking cube root of [tex] 8^{x} [/tex]. Cube root is equivalent to raising the power to [tex] \frac{1}{3} [/tex].
So, we can say we raising [tex] 8^{x} [/tex] to the power [tex] \frac{1}{3} [/tex].
In expression form, this will be:
[tex] ( 8^{x} )^{ \frac{1}{3} } \\ \\
= 8^{ \frac{x}{3} } [/tex]
Therefore, third option is the correct answer