Answer
a)$6\sqrt[3] 3$
b)$\frac{3\sqrt 2}{ 5}$
c)$\frac{2\sqrt 3}{7}$
Work Step by Step
a) $2\sqrt[3] {81}=2\times (9^{2})^{\frac{1}{3}}=2\times (3^{4})^{\frac{1}{3}}=6\sqrt[3] 3$
b) $\frac{\sqrt {18}}{\sqrt {25}}=\frac{\sqrt 9\times\sqrt 2}{\sqrt {25}}=\frac{3\sqrt 2}{ 5}$
c) $\sqrt {\frac{12}{49}}=\frac{\sqrt {4\times3}}{\sqrt {49}}=\frac{{\sqrt 4}\times\sqrt 3}{7}=\frac{2\sqrt 3}{7}$
