The mathematical equation relating the independent variable to the expected value of the dependent variable; that is, e(y) = ? 0 + ? 1x, is known as

Equations relating an independent variable to a dependent variable is a function. 

Simply put, the independent variable is the input variable, most often x. The dependent variable, or output variable, is the one for which the equation must be evaluated for a given x, is usually a y. In function notation, we swap out y for f(x).