Ta có: \(\frac{2\cdot6\cdot12+6\cdot12\cdot20+12\cdot21\cdot32}{3\cdot8\cdot15+9\cdot16\cdot25+18\cdot28\cdot40}\)
\(=\frac{2^2\cdot6^2+2^2\cdot6^2\cdot10+2^2\cdot6^2\cdot7\cdot2^3}{3^2\cdot8\cdot5+3^2\cdot8\cdot5\cdot10+3^2\cdot8\cdot5\cdot56}\)
\(=\frac{2^2\cdot6^2\left(1+10+56\right)}{3^2\cdot8\cdot5\left(1+10+56\right)}=\frac{2^2\cdot6^2}{3^2\cdot8\cdot5}\)
\(=\frac{2^2\cdot3^2\cdot2^2}{3^2\cdot2^3\cdot5}=\frac{2^4}{2^3\cdot5}=\frac{2^3\cdot2}{2^3\cdot5}=\frac{2}{5}\)