Simplify \(21\times 6\) to \(126\).
\[\sqrt{126\times 7\times 8}\]
Simplify \(126\times 7\) to \(882\).
\[\sqrt{882\times 8}\]
Simplify \(882\times 8\) to \(7056\).
\[\sqrt{7056}\]
Since \(84\times 84=7056\), the square root of \(7056\) is \(84\).
\[84\]
84
