Get more lessons like this at http://www.MathTutorDVD.com. Here you will learn what a function is in math, the definition of a function, and why they are important. Functions have applications in algebra, calculus, science, and engineering. We first begin by describing a function as a mathematical machine that takes input numbers "x" and computes output numbers "f(x)". We then describe the input numbers "x" as being the domain of the function, while the output numbers f(x) are the range of the function. We will plot several functions including linear functions, quadratic functions, cubic functions, and more.