Question

What is the factorial of $9$ ?

Answer 1

Determine the $9!$.

Calculate the factorial of $9$:

$\begin{array}{rcl}9!& =& 9\times 8\times 7\times 6\times 5\times 4\times 3\times 2\times 1\\ & \Rightarrow & 9!=362880\end{array}[\because \mathit{n}\mathbf{!}\mathbf{=}\mathit{n}\mathbf{(}\mathbf{n}\mathbf{-}\mathbf{1}\mathbf{)}\mathbf{(}\mathbf{n}\mathbf{-}\mathbf{2}\mathbf{)}\mathbf{\dots }\mathbf{\dots }\mathbf{\dots }\mathbf{\left(}\mathbf{3}\mathbf{\right)}\mathbf{\left(}\mathbf{2}\mathbf{\right)}\mathbf{\left(}\mathbf{1}\mathbf{\right)}\mathbf{}\mathbf{,}\mathbf{}\mathbf{}\mathit{n}\mathbf{\ge }\mathbf{1}\mathbf{,}\mathbf{}\mathit{n}\mathbf{\in }\mathit{N}\mathbf{]}$

Hence, the required factorial is $\begin{array}{l}9!=362880\end{array}$.