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# What is the binomial theorem?

474849 ###### 2005-11-02 00:13:52

In mathematics, the binomial theorem is an important formula giving the expansion of powers of sums. Its simplest version reads (x+y)^n=\sum_{k=0}^n{n \choose k}x^ky^{n-k}\quad\quad\quad(1) whenever n is any non-negative integer, the numbers {n \choose k}=\frac{n!}{k!(n-k)!} are the binomial coefficients, and n! denotes the factorial of n. This formula, and the triangular arrangement of the binomial coefficients, are often attributed to Blaise Pascal who described them in the 17th century. It was, however, known to Chinese mathematician Yang Hui in the 13th century. For example, here are the cases n = 2, n = 3 and n = 4: (x + y)^2 = x^2 + 2xy + y^2\, (x + y)^3 = x^3 + 3x^2y + 3xy^2 + y^3\, (x + y)^4 = x^4 + 4x^3y + 6x^2y^2 + 4xy^3 + y^4.\, Formula (1) is valid for all real or complex numbers x and y, and more generally for any elements x and y of a semiring as long as xy = yx.

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## Related Questions The binomial theorem describes the algebraic expansion of powers of a binomial: that is, the expansion of an expression of the form (x + y)^n where x and y are variables and n is the power to which the binomial is raised. When first encountered, n is a positive integer, but the binomial theorem can be extended to cover values of n which are fractional or negative (or both). Binomial Theorem consists of formulas to determine variables. In pharmacy it can be used to calculate risks and costs of certain medications. It's better to think about the ordinary binomial theorem first. Consider a binomial (x + y), and raising it to a power, say squaring it. (x + y)^2 = (x + y)(x + y) = x^2 + 2xy + y^2 Now try cubing it. (x + y)^3 = (x + y)(x + y)(x + y) = x^3 + 3x^2 y + 3xy^2 + y^3 It becomes very tedious to do this. The binomial theorem allows us to expand binomial expressions to a power very quickly. The generalised binomial theorem is, as it says, 'generalised' - the 'original' binomial theorem only allows us to expand binomial expressions to a power which is a whole number (0, 1, 2, 3 ... etc) but not numbers such as 1/2, 1/3 or -1. Newton's generalised binomial theorem allows us to expand binomial expressions for any _rational_ power. (that is any number which can be expressed as a ratio of two integers - not something horrible like the cube root of three) So now we can expand things like (x + y)^0.5, (1 - x)^-1 and all that malarky - this has some fairly deep significances, such as allowing numerical approximations of surds and bears relevance to some power series. For example, take (1 - x)^-4, using Newton's generalised binomial theorem it can be seen that (1 - x)^-4 = 1 + 4x + 10x^2 + 20x^3 ... Each expansion for a rational exponent of the binomial expressions creates an infinite series. The actual calculations are best left to a site which can show you the mathematical notation, but if you can do the normal binomial theorem - the nuances of this one will be easy to grap. In different countries you learn it at different grades. Your question needs to specify which country - or even region - your question is about. We often come across the algebraic identity (a + b)2 = a2 + 2ab + b2. In expansions of smaller powers of a binomial expressions, it may be easy to actually calculate by working out the actual product. But with higher powers the work becomes very cumbersome.The binomial expansion theorem is a ready made formula to find the expansion of higher powers of a binomial expression.Let ( a + b) be a general binomial expression. The binomial expansion theorem states that if the expression is raised to the power of a positive integer n, then,(a + b)n = nC0an + nC1an-1 b+ nC2an-2 b2+ + nC3an-3 b3+ ………+ nCn-1abn-1+ + nCnbnThe coefficients in each term are called as binomial coefficients and are represented in combination formula. In general the value of the coefficientnCr = n!r!(n-r)!It may be interesting to note that there is a pattern in the binomial expansion, related to the binomial coefficients. The binomial coefficients at the same position from either end are equal. That is,nC0 = nCn nC1 = nCn-1 nC2 = nCn-2 and so on.The advantage of the binomial expansion theorem is any term in between can be figured out without even actually expanding.Since in the binomial expansion the exponent of b is 0 in the first term, the general term, term is defined as the (r+1)th b term and is given by Tr+1 = nCran-rbrThe middle term of a binomial expansion is [(n/2) + 1]th term if n is even. If n is odd, then terewill be two middle terms which are [(n+1)/2]th and [(n+3)/2]th terms.

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