\displaystyle [br]\begin{equation*}n! = n\underbrace{(n-1)(n-2)(n-3)\cdots (2)(1)}_{(n-1)!}\end{equation*}
\displaystyle [br]\begin{equation*} n!=n(n-1)\underbrace{(n-2)\cdots (2)(1)}_{(n-2)!} = n(n-1)(n-2)! \end{equation*}
\displaystyle [br]\begin{equation*}n! = n\underbrace{(n-1)(n-2)(n-3)\cdots (2)(1)}_{(n-1)!}\end{equation*}
\displaystyle [br]\begin{equation*} n!=n(n-1)\underbrace{(n-2)\cdots (2)(1)}_{(n-2)!} = n(n-1)(n-2)! \end{equation*}