[tex]~\hspace{7em}\textit{rational exponents} \\\\ a^{\frac{ n}{ m}} \implies \sqrt[ m]{a^ n} ~\hspace{10em} a^{-\frac{ n}{ m}} \implies \cfrac{1}{a^{\frac{ n}{ m}}} \implies \cfrac{1}{\sqrt[ m]{a^ n}} \\\\[-0.35em] \rule{34em}{0.25pt}[/tex]
[tex]\boxed{A}\qquad \sqrt[4]{8}\implies \sqrt[4]{2^3}\implies 2^{\frac{3}{4}} \\\\\\ \boxed{B}\qquad \sqrt[4]{2^3}\implies 2^{\frac{3}{4}} \\\\\\ \boxed{C}\qquad 2^{\frac{1}{4}}\times 2^{\frac{1}{2}}\implies 2^{\frac{1}{4}+\frac{1}{2}}\implies 2^{\frac{1+2}{4}}\implies 2^{\frac{3}{4}} \\\\\\ \boxed{D}\qquad \left( 2^{\frac{1}{4}} \right)^{\frac{1}{2}}\implies 2^{\frac{1}{4}\cdot \frac{1}{2}}\implies 2^{\frac{1}{8}}\qquad \textit{\large \checkmark}[/tex]
