# WHY ZERO FACTORIAL IS ONE

## WHY ZERO FACTORIAL IS ONE

Ironically, the concept of zero factorial being one is not as trivial as it might seem at first glance. It is a fascinating idea that requires a comprehensive understanding of factorials, their mathematical properties, and the underlying reasons for this unique value. Let's delve into the intriguing world of factorials and uncover the logic behind this seemingly counterintuitive notion.

### Understanding Factorials

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. This concept finds extensive applications in various fields, including probability, combinatorics, and calculus. The factorial of an integer n is defined as follows:

n! = n × (n-1) × (n-2) × … × 3 × 2 × 1

For example:

• 5! = 5 × 4 × 3 × 2 × 1 = 120
• 4! = 4 × 3 × 2 × 1 = 24
• 3! = 3 × 2 × 1 = 6

### The Unique Case of Zero Factorial

By definition, 0! is equal to the product of all positive integers less than or equal to zero. However, there are no positive integers less than or equal to zero. This peculiar situation poses a unique challenge in defining the factorial of zero.

Mathematicians and scientists have grappled with this dilemma for centuries, and the most widely accepted solution is to assign a value of one to zero factorial. This seemingly arbitrary choice is not without its logic and profound implications.

### Mathematical Justification for 0! = 1

The assignment of 0! to one finds strong support in various mathematical contexts. Here are a few key reasons:

1. Factorial as a Counting Function: Factorials are often used to count the number of distinct permutations or arrangements of a set of objects. For instance, 3! represents the number of ways to arrange three distinct objects in a specific order. If we were to consider the scenario of arranging zero objects, there is only one possible arrangement: an empty set. Assigning a value of one to 0! ensures that this fundamental counting principle holds true.

2. Factorial and Gamma Function: The gamma function, denoted by Γ(z), is a generalization of the factorial function to complex numbers. The gamma function is defined as:

Γ(z) = ∫0^∞ t^(z-1)e^(-t) dt

It is worth noting that Γ(n+1) = n! for all non-negative integers n. This relationship between the gamma function and the factorial function provides a bridge between continuous and discrete mathematics. Assigning a value of one to 0! allows for a smooth transition between these two mathematical domains.

### Significance of 0! = 1 in Probability and Statistics

The assignment of 0! to one has significant implications in probability and statistics. Here's why:

1. Probability of an Empty Event: In probability, the probability of an event occurring is a number between 0 and 1, inclusive. The probability of an impossible event is 0, while the probability of a certain event is 1. If we consider the event of selecting zero items from a set, the probability of this event occurring is 1. This is because there is only one way to select zero items: by not selecting anything. Assigning a value of one to 0! ensures that the probability of this event is correctly calculated.

2. Binomial Distribution: The binomial distribution is a discrete probability distribution that describes the number of successes in a sequence of independent experiments, each of which has a constant probability of success. The binomial distribution is defined as follows:

P(X = k) = (n k) * p^k * (1-p)^(n-k)

where:

• n is the number of experiments
• k is the number of successes
• p is the probability of success in each experiment

It is interesting to note that the binomial distribution reduces to a special case when n = 0. In this case, the probability of obtaining exactly zero successes is 1, regardless of the value of p. This property holds true because 0! is defined as 1.

### Conclusion

The assignment of 0! to one is a well-established convention in mathematics, probability, and statistics. This seemingly arbitrary choice is rooted in sound mathematical principles and has profound implications in various fields. It ensures consistency in counting principles, provides a bridge between continuous and discrete mathematics, and allows for accurate calculations in probability and statistics.

1. Why is zero factorial defined as one?

• Assigning one to zero factorial ensures consistency in counting principles, provides a smooth transition between continuous and discrete mathematics, and allows for accurate calculations in probability and statistics.
2. What are the applications of zero factorial?

• Zero factorial finds applications in various fields, including combinatorics, probability, and statistics. It is used in counting problems, calculating probabilities, and deriving formulas in mathematical analysis.
3. Is there an alternative definition for zero factorial?

• No, the definition of zero factorial as one is universally accepted in mathematics and statistics. Alternative definitions would lead to inconsistencies and inaccuracies in mathematical calculations.
4. What happens if we define zero factorial as a different value?

• Defining zero factorial as a value other than one would have significant implications in various mathematical and statistical applications. It would lead to incorrect results and inconsistencies in calculations, making it an impractical choice.
5. Can zero factorial be negative?

• No, zero factorial is always a non-negative integer. By definition, factorials are products of positive integers, and multiplying any number of positive integers always results in a non-negative value.