The given expression in simplified form are:
1) [tex] \sqrt[7]{12} =12 ^{\frac{1}{7}} [/tex]
2)[tex] (\sqrt[7]{3})^{4} =3^{\frac{4}{7}} [/tex]
3) [tex] \sqrt[7]{81} =81^{\frac{1}{7}} =3^{\frac{4}{7}} [/tex]
4)[tex] \sqrt[4]{21} =21^{\frac{1}{4}} [/tex]
5) [tex] \sqrt[4]{3^{7}} =3^{\frac{7}{4}} [/tex]
6)[tex] \sqrt[4]{3^{7}} =3^{\frac{7}{4}} [/tex]
Among all the options option 2 and 3 are the right one.
