Asymptote

Closer and closer and closer…a line that a graph approaches but never touches.

Combined Variation

A relationship between three variables that combines or merges direct variation and inverse variation. Here's the general form:

Domain

"D" is for domain, where the denominator doesn't equal diddly (by that, we mean the denominator isn't zero). The domain is just all the possible x-values a rational function can take.

Direct Variation

A relationship between two variables that are directly proportional; when one increases, the other does too, and vice versa. The general form looks like this guy right here, where k is the constant of variation:

y = kx

Extraneous Solution

A false solution to an equation. It makes the equation blow up because the denominator is zero.

Intercept

For all you sports nuts—think football. It's the point where a graph "takes," "seizes," or "crosses" an axis.

Inverse Variation

A relationship between two variables that are inversely proportional. In other words, as x increases, y decreases, and vice versa. Here's what that looks like in equation form, where k is the constant of proportionality:

Joint Variation

Joint = together. It's a relationship where one variable is directly proportional to two other variables at the same time, with a constant of variation (k) thrown in for good measure. Here's the equation:

y = kxz

Rational Equation

Keep an eye out for "ratios" and an "=" sign. This is an equation involving one or more rational expressions.

Rational Expression

An expression with a polynomial in the numerator and another polynomial in the denominator. For the expression to be defined, the polynomial in the denominator must be non-zero. You know how grumpy mathematicians get about dividing by zero.

Rational Function

"Rational" = ratio. This is a function that's equal to the ratio of two polynomials.

Reciprocal

A "flipped" or inverted fraction. Watch out for the zeros in the denominator.