Answer
$\color{blue}{\sqrt[3]{2}}$
Work Step by Step
RECALL:
$\sqrt[m]{\sqrt[n]{a}}=\sqrt[mn]{a}$
Use the rule above to obtain:
$=\sqrt[3(2)]{4}
\\=\sqrt[6]{4}$
Since $4=2^2$, the expression above is equivalent to:
$=\sqrt[6]{2^2}$
Use the rule $\sqrt[n]{a^m}=a^{m/n}$ to obtain:
$=2^{2/6}
\\=2^{1/3}$
Use the rule $a^{1/n} = \sqrt[n]{a}$ to obtain:
$=\color{blue}{\sqrt[3]{2}}$
