### Definition of Quadratic Expressions

A quadratic expression is an algebraic expression having a degree of 2.

### Identifying One Variable Quadratic Expressions

An algebraic expression in one variable is quadratic when:

- The variable has an exponent of 2 on it
- The variable does not have an exponent greater than 2
- The variable does not have a negative exponent

In simple words the above three statements mean:

- There is at least one term in the expression with `x^2` in it
- There is no term in the expression with `x^3` or higher exponents in it
- The expression does not have `x` in the denominator

#### Example

The algebraic expression `x^2 + 2x + 3` is quadratic because

- 'x' has an exponent of '2' on it
- 'x' does not have an exponent greater than 2 on it, and
- 'x' has an exponent of 1 in the term '2x' and an exponent of 0 in the term '3'

#### Counter Examples

- The expression `x^3 + 3x^2` is not quadratic because 'x' has an exponent greater than 2 in it.
- The expression `x^2 + 1/x` is not quadratic because 'x' is in the denominator (and hence has negative exponents)
- The expression `0x^2 + 3x + 2` is not quadratic because there is no term with `x^2` in it (the term `0x^2` equals 0 so it is not considered)

### Identifying Two Variable Quadratic Expressions

A quadratic expression can have two variables, given that

- the sum of exponents of both variables in any term is never greater than 2, and
- there is at least one term whose degree is 2
- no variable is present with a negative exponent

#### Example

`x^2 + xy + y^2` is a quadratic expression because

- `x` and `y` do not have exponents greater than 2 in any term
- sum of exponents of x and y in the term `xy` is 2

#### Counter Examples

- `x^2y + xy + 1` is not a quadratic expression because the sum of exponents of `x` and `y` in the term `x^2y` is 3, which is greater than 2
- `x/y + x^2` is not a quadratic expression because `y` is in the denominator, thus making it a rational expression

What formula would I use for x^4-x^3+27x-27

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