Functions are one of the most important additions to the Math section of the new SAT. So, what’s a function? A function describes a relationship between one or more inputs and one output. The inputs to a function are variables such as x; the output of the function for a particular value of x is usually represented as f(x) or g(x). In the function f(x) = 2x, the output of the function is always equal to two times the value of x. So, if x = 1, then f(x) = 2, and if x = 12, then f(x) = 24.

So far, it may seem as if a function is just another word for equation. Based on the way the SAT generally tests functions, it’s fine to think of functions that way. However, all functions follow a special rule that you’ve got to know:

You might be asking yourself what this math babble means. Here’s an example that should help translate. Take the equation |y| = x. Because y sits between absolute value brackets, if x = 2, then y could be equal to either 2 or –2. This equation can’t be a function, because for each value of x, there are two possible values of y.