a) Ta có: \(\left(-16\right)\cdot81\cdot\left(-625\right)\)
\(=16\cdot625\cdot81\)
\(=2^4\cdot5^4\cdot3^4\)
\(=\left(2\cdot5\cdot3\right)^4=30^4\)
b) Ta có: \(64\cdot25\cdot\left(-5\right)\)
\(=4^3\cdot\left(-5\right)^3\)
\(=\left(-20\right)^3\)