### Asymptote

Closer and closer and closerâ€¦a line that a graph approaches but never touches.

### Combined Variation

Combines or merges direct variation (one goes up the other goes up) and inverse variation (one goes up the other goes down).

### Domain

"D" is for domain, where the denominator doesn't equal diddly (by that, we mean the denominator isn't zero).

### Direct Variation

An equation with a constant (

*k*) where one goes up, the other goes up, or one goes down, the other goes down.

* y* =

*kx*### Extraneous Root

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

### Intercept

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

### Inverse Variation

An equation with a constant (

*k*) where one goes up, the other goes down, or one goes down, the other goes up.

* *### Joint Variation

Joint = together. It's an equation with a constant (

*k*) where one depends on two variables together.

* z* =

*kxy*### Rational Equation

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

### Rational Expression

"Rational" = ratio. This is the ratio of two polynomials.

### Rational Function

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

### Reciprocal

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