Polynomials
A polynomial is made up of terms that are only added, subtracted or multiplied.
A polynomial looks like this:
 |
| example of a polynomial this one has 3 terms |
Polynomial comes form poly- (meaning "many") and -nomial (in this case meaning "term") ... so it says "many terms"
A polynomial can have:
| constants (like 3, -20, or ½) |
| variables (like x and y) |
| exponents (like the 2 in y2), but only 0, 1, 2, 3, ... etc |
and they can be combined using:
| + | addition, |
| - | subtraction, and |
| × | multiplication |
 ... but not division! |
Those rules keeps polynomials simple, so they are easy to work with!
Polynomial or Not?
These are polynomials:
- 3x
- x - 2
- -6y2 - (7/9)x
- 3xyz + 3xy2z - 0.1xz - 200y + 0.5
- 512v5+ 99w5
- 1
(Yes, even "1" is a polynomial, it has one term which just happens to be a constant).
And these are not polynomials
- 2/(x+2) is not, because dividing is not allowed
- 1/x is not
- 3xy-2 is not, because the exponent is "-2" (exponents can only be 0,1,2,...)
- √x is not, because the exponent is "½" (see fractional exponents)
But these are allowed:
- x/2 is allowed, because it is also (½)x (the coefficient is ½, or 0.5)
- also 3x/8 for the same reason (the coefficient is 3/8, or 0.375)
- √2 is allowed, because it is a constant (= 1.4142...etc)
Monomial, Binomial, Trinomial
There are special names for polynomials with 1, 2 or 3 terms:
| How do you remember the names? Think cycles! |
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(There is also quadrinomial (4 terms) and quintinomial (5 terms),
but those names are not often used)
Can Have Lots and Lots of Terms
Polynomials can have as many terms as needed, but not an infinite number of terms.
Variables
Polynomials can have no variable
Example: 21 is a polynomial. It has just one term, which is a constant.
Or one variable
Example: x4-2x2+x has three terms, but only one variable (x)
Or two or more variables
Example: xy4-5x2z has two terms, and three variables (x, y and z)
What is Special About Polynomials?
Because of the strict definition, polynomials are easy to work with.
For example we know that:
- If you add polynomials you get a polynomial
- If you multiply polynomials you get a polynomial
So you can do lots of additions and multiplications, and still have a polynomial as the result.
Also, polynomials of one variable are easy to graph, as they have smooth and continuous lines.
Example: x4-2x2+x
 |
See how nice and |
Degree
The degree of a polynomial with only one variable is the largest exponent of that variable.
Example:
 |
The Degree is 3 (the largest exponent of x) |
For more complicated cases, read Degree (of an Expression).
Standard Form
The Standard Form for writing a polynomial is to put the terms with the highest degree first.
Example: Put this in Standard Form: 3x2 - 7 + 4x3 + x6
The highest degree is 6, so that goes first, then 3, 2 and then the constant last:
x6 + 4x3 + 3x2 - 7
You don't have to use Standard Form, but it helps.