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We define the factorial of a number as the multiplication of all integers from that number to 1.
We use the symbol ! which is an exclamation mark to denote factorial and we put the exclamation mark next to a number.
For example, 5! is read as five factorial and we can evaluate 5! by multiplying all integers from 5 to 1.
5! = 5 × 4 × 3 × 2 × 1 = 20 × 6 = 120
Let n be a whole number, then n! read as n factorial represents the product of all whole number from n to 1
In other words, n! = n×(n - 1)×(n - 2)×(n - 3) ... 3×2×1
By definition 0! = 1 and 1! = 1
Evaluating factorials
1) Evaluate 6!
To evaluate 6!, find the product of all whole numbers from 6 to 1
6! = 6 × 5 × 4 × 3 × 2 × 1 = 20 × 6 = 720
Notice that we have already computed 5! and 5! = 120. Therefore you could have just multiplied 120 by 6 to get 6 factorial.
6! = 6 × 5!
In general, n! = n × (n -1)!
Evaluate (8 - 3)!
(8 - 3)! = 5! = 120