# Binomial Coefficient

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### Binomial Coefficient Formula

The binomial coefficient is represented as $$\binom{n}{k}$$, which is read as "n choose k". This formula describes the number of combinations in which $$k$$ elements can be chosen from $$n$$ elements regardless of order:

$\binom{n}{k} = \frac{n!}{k!(n-k)!}$

Where $$n!$$ denotes the factorial of $$n$$.

### Examples of Binomial Coefficient Applications

• Combinatorics

The binomial coefficient is used to calculate the number of combinations, which means the ways to select a group of elements from a larger set. For example, if you have a class of 20 students and you want to choose 3 people for a sports team, the binomial coefficient helps to determine how many different teams can be formed.

$\newcommand\ccancel[2][black]{\color{#1}{\cancel{\color{black}{#2}}}} \binom{20}{3} = \frac{20!}{3!(20-3)!} = \frac{20!}{3!\cdot17!} = \frac{{\ccancel[red]{17!}} \cdot 18\cdot 19\cdot 20}{6\cdot \ccancel[red]{17!}} = \frac{6840}{6} = 1140$

• Algebra

In algebra, the binomial coefficient is used in expanding binomial expressions. The binomial theorem is a way of expanding expressions of the type $$(a + b)^n$$ into a sum of terms containing powers of $$a$$ and $$b$$. This allows us to quickly calculate the values of such expressions without performing complex multiplications.

• Statistics

In statistics, the binomial coefficient is useful in analyzing probability distributions. For example, if you want to calculate the probability of obtaining a certain number of successes in a series of trials (e.g., coin tosses), the binomial coefficient allows for quick computation.

• Probability Theory

The binomial coefficient is also crucial in theoretical considerations of the probability of various events. It helps in modeling and understanding how often certain combinations of events may occur.