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Polynomial Characteristics

What Makes a Polynomial?

In algebra, we work with all sorts of expressions. A polynomial is a special type. Think of it as an expression built from variables and coefficients, using only addition, subtraction, and multiplication, where the variable is raised to non-negative integer powers.

The key rule for an expression to be a polynomial in one variable (like xx) is that the exponents of the variable must be [{}] (0, 1, 2, 3, and so on). No fractions or negative numbers allowed in the exponent!

Let's break down an example: $4x^3 - 2x + 7$.

This polynomial is made up of individual parts called terms, which are separated by plus or minus signs. The terms here are $4x^3$, $-2x$, and $7$.

Within each term, the number part is called the coefficient. In $4x^3$, the coefficient is 4. In $-2x$, it's -2. The term without a variable, 7, is called the constant term.

ExpressionIs it a Polynomial?Why?
5x23x+15x^2 - 3x + 1YesAll exponents (2, 1, and 0 for the constant term) are whole numbers.
y4+2y^4 + \sqrt{2}YesThe exponent on yy is 4. 2\sqrt{2} is just a coefficient.
x+1xx + \frac{1}{x}NoThe term 1x\frac{1}{x} is the same as x1x^{-1}, which has a negative exponent.
3t43\sqrt{t} - 4NoThe term t\sqrt{t} is the same as t1/2t^{1/2}, which has a fractional exponent.

Special Cases

Most polynomials have variables, but not all. A number by itself, like 5, is also a polynomial. It's called a constant polynomial. You can think of it as 5x05x^0, and since x0=1x^0 = 1, it simplifies to just 5.

The number 0 is also a polynomial, but it's a very special case called the because it has some unique properties that set it apart from all other constants.

Classifying Polynomials

We can categorize polynomials in two main ways: by how many terms they have, and by their degree.

Degree

noun

The highest exponent of the variable in a polynomial.

The degree tells us the general shape and complexity of the polynomial's graph. Based on the degree, we have special names for the most common types.

DegreeNameExample
1Linear2x+12x + 1
2Quadraticx23x+2x^2 - 3x + 2
3Cubic4x35x4x^3 - 5x
0Constant77

We also classify polynomials by their number of terms.

Number of TermsNameExample
1Monomial5x25x^2
2Binomialx3x - 3
3Trinomialx2+6x+9x^2 + 6x + 9

An expression can be classified both ways. For example, x24x^2 - 4 is a quadratic binomial. It's quadratic because its degree is 2, and it's a binomial because it has two terms. What about 8x38x^3? That's a cubic monomial.

Quiz Questions 1/6

Which of the following expressions is a polynomial?

Quiz Questions 2/6

In the polynomial 5x48x2+x35x^4 - 8x^2 + x - 3, what is the coefficient of the x2x^2 term?