A factorial, represented as (where is an integer), is equal to the product of itself and all integers less than it until you get to one. Represented mathematically, we could say:
When we use the formula, we can find 4!, as shown below:
The reason is because it is not just 6 it is - 6 so when there are two negative numbers they don't subtract they add if it was 6n then it was to be subtracted