0! = 1 how?
We know that factorial of a number can be written as product of that number and factorial of its previous number. That is:
n! = n × (n - 1)!
This can also be written as ratio of the given number’s factorial and the same number. It will be equal to factorial of its previous number as shown below:
n!n = (n - 1)!
When the given number is taken as 1, it will be equal to its previous number’s factorial i.e. 0!.
For n = 1, so 1!1 = (1 - 1)! = 0!
Hence, 0! = 1.