Tool to calculate the values of the binomial coefficient (combination choose operator) used for the development of the binomial but also for probabilities and counting.
Binomial Coefficient - dCode
Tag(s) : Combinatorics
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The binomial coefficient is a number that represents the number of ways to choose $ k $ elements from $ n $ distinct elements, regardless of order. In other words, it measures the number of possible combinations (counting).
The binomial coefficient is noted $ {n \choose k} $ or $ C_{n}^{k} $ is read $ n $ choose $ k $ (or $ k $ among $ n $). Generally $ n $ is the total number of elements and $ k $ is the number of chosen elements.
The binomial coefficient and is defined by the formula $$ {n \choose k} = \frac{n!}{k!(n-k)!} $$ with $ n! $ the factorial of n.
In practice, factorials have values that simplify.
Example: $ {10 \choose 6} = \frac{10!}{6!4!} = \frac{10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1}{6 \times 5 \times 4 \times 3 \times 2 \times 1 \times 4 \times 3 \times 2 \times 1} = \frac{10 \times 9 \times 8 \times 7 }{4 \times 3 \times 2 \times 1} = \frac{5040}{24} = 210 $
The values of the binomial coefficient appear in the development of the Newton binomial:
$$ (a+b)^{n}=\sum_{k=0}^{n}{n \choose k}a^{{n-k}}b^{k} $$
Example: $$ (x+y)^{4} = x^4 + {4 \choose 1} x^3 y + {4 \choose 2} x^2 y^2 + {4 \choose 3} x y^3 + y^4 = x^4 + 4 x^3 y + 6 x^2 y^2 + 4 x y^3 + y^4 $$
The value of the binomial coefficient $$ \binom{A}{B} $$ is found in Pascal's triangle at row A, column column B (in row and column are 0-indexed).
The following formulas can be useful for binomial coefficients:
$$ {n \choose k} = {n \choose n-k} $$
$$ {n \choose k} + {n \choose k+1} = {n+1 \choose k+1} $$
$$ {n \choose k} = {\frac{n}{k}}{n-1 \choose k-1} $$
$$ {n \choose 0} = 1 $$
$$ {n \choose n} = 1 $$
The binomial coefficient is used primarily in count and probability calculations. This is the basis for calculating the number of combinations of k elements out of n.
Example: The number of lotto combinations is 5 out of 49 ie $ {49 \choose 5} = 1906884 $ possible combinations.
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Binomial Coefficient on dCode.fr [online website], retrieved on 2024-12-02,