Cho biểu thức $\sqrt[3]{\frac{2}{5}\cdot \sqrt[7]{\frac{2}{5}\cdot \sqrt[3]{\frac{2}{5}}}}\cdot \frac{2}{5}$

a) Đúng; b) Sai; c) Đúng; d) Đúng.
Ta có: $\sqrt[3]{\frac{2}{5}\cdot \sqrt[7]{\frac{2}{5}\cdot \sqrt[3]{\frac{2}{5}}}}\cdot \frac{2}{5}=\sqrt[3]{\frac{2}{5}\cdot \sqrt[7]{\frac{2}{5}\cdot {\left(\frac{2}{5}\right)}^{\frac{1}{3}}}}\cdot \frac{2}{5}=\sqrt[3]{\frac{2}{5}\cdot \sqrt[7]{{\left(\frac{2}{5}\right)}^{\frac{4}{3}}}}\cdot \frac{2}{5}$ $$=\sqrt[3]{\frac{2}{5}\cdot {\left(\frac{2}{5}\right)}^{\frac{4}{21}}}\cdot \frac{2}{5}={\left(\frac{2}{5}\right)}^{\frac{25}{63}}\cdot \frac{2}{5}={\left(\frac{2}{5}\right)}^{\frac{88}{63}}.$$
a) a) Đúng.
b) b) Sai.
c) c) Đúng.
d) d) Đúng.