A polynomial (in a variable ) is a function or an expression that can be evaluated by combining the variable and possibly some constants by a finite number of additions, subtractions, and multiplications. Note that the list excludes divisions (although a number like would be considered a constant). Also excluded are radicals like although a number like would be (again) considered a constant. When it matters we use the phrases polynomial expression or polynomial function, but more frequently we use just the word polynomial by itself.
A polynomial can always be written in standard form as
The function is also a polynomial. It is called the zero polynomial (or the zero function.) Its degree is undefined, , or , depending on the author. You don't have to worry about the degree of the zero polynomial in this class.
Some examples will illustrate these concepts:
Don't get distracted by the subtlety of some of these examples. Usually it will be true that if you see a radical, an absolute value, or a division by an algebraic expression, then the expression or function in question is not a polynomial. But it is important to understand and appreciate the definition of the term polynomial with all its subtleties and ramifications.
Polynomials are important because they occur in applications and they have nice properties: they are defined for all values of the variable, and their graphs are smooth. Indeed, polynomials occur so frequently that there is a whole language associated with them. The terms involved are defined here, and you can also find their definitions in virtually any ordinary dictionary of the English language. Throughout let be defined as in above, with .
You can add, subtract, and multiply polynomials and get a new polynomial. On the other hand, the ratio of two polynomials is usually not a polynomial. Rather than memorizing a number of rules for the various operations you should recognize that they are just the ordinary rules underlying all algebra, such as the distributive law and the commutative and associative laws of multiplication and addition. A few examples illustrate the idea.
Let
Remember that you multiply powers with the same base by adding the exponents. This implies that the degree of the product of two polynomials is the sum of the individual degrees. If you add (or subtract) two polynomials of different degrees then the degree of the sum (or difference) is the larger of the two individual degrees. If the two polynomials have the same degrees then the degree of the sum or difference is that same degree unless the leading coefficients cancel, in which case the degree of the sum or difference is less. Don't attempt to memorize these facts, instead make up some examples, think about the mechanism of the operation, and then work out the details from your understanding when you need them.