remember
[tex]x^ \frac{m}{n} = \sqrt[n]{x^m} [/tex]
and
[tex](zy)^m=(z^m)(y^m)[/tex]
and
(x^m)^n=x^(mn)
so
[tex] ((7x^3)(y^2))^ \frac{2}{7} = \sqrt[7]{((7x^3)(y^2))^2} [/tex]=
[tex] \sqrt[7]{((7x^3)^2(y^2)^2)} [/tex]=
[tex] \sqrt[7]{((7^2x^6)(y^4))} [/tex]=
[tex] \sqrt[7]{((49x^6)(y^4))} [/tex]=
[tex] \sqrt[7]{49x^6y^4} [/tex]
