What Is a Binomial?

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A polynomial equation with two terms usually joined by a plus or minus sign is called a binomial. Binomials are used in algebra. Polynomials with one term will be called a monomial and could look like 7x. A polynomial with two terms is called a binomial, it could look like 3x + 9. It is easy to remember binomials as bi means 2 and a binomial will have 2 terms.

A classic example is the following: 3x + 4 is a binomial and is also a polynomial,  2a(a+b) is also a binomial (a and b are the binomial factors).

The above are both binomials.

When multiplying binomials, you'll come across a term called the FOIL method which is often just the method used to multiply binomials. 

For instance, to find the product of 2 binomials, you'll add the products of the First terms, the Outer terms, the Inner terms, and the Last terms.

When you're asked to square a binomial, it simply means to multiply it by itself. The square of a binomial will actually be a trinomial. The product of two binomials will be a trinomial.

Example of Multiplying Binomials


   (5 + 4x) x (3 + 2x)
   (5 + 4x)(3 + 2x)
= (5)(3) + (5)(2x) + (4x)(3) + (4x)(2i)
= 15 + 10x + 12x + 8(x)2 = 15 + 22x + 8(-1)
= 15 + 22x - 8 = (15 - 8) + 22x = 7 + 22x

Once you begin taking algebra in school, you'll be doing a great many computations that require binomials and polynomials.

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Russell, Deb. "What Is a Binomial?" ThoughtCo, Jan. 23, 2018, thoughtco.com/definition-of-binomial-2312369. Russell, Deb. (2018, January 23). What Is a Binomial? Retrieved from https://www.thoughtco.com/definition-of-binomial-2312369 Russell, Deb. "What Is a Binomial?" ThoughtCo. https://www.thoughtco.com/definition-of-binomial-2312369 (accessed February 18, 2018).