 Let's consider a function definition in Algebra. You can think of a function as a black box that takes some input and provides some output. The x in our function definition is a parameter. When we apply the function, in this case by calculating f of 1.5, 1.5 is the argument of the function. It's the input to our black box. The result of applying the function, the output from the black box, can be assigned to a different algebraic variable, in this case y. The Java term for a function is a method. How do we make an equivalent method in Java? First, we start off with a modifier. For now, we will always be using public static, more on that later in the course. We then give the name of the method and our parameter name. Here's where we part company with the world of algebra. In algebra, we just sort of know that the domain and range of f is the real numbers. In Java, we must specify the type of the parameter and also the type of the value that the method returns. In the body of the method, we calculate the result and use the return statement to send back the result. In algebra, you apply a function. In Java, we call a method. Here's an example of a method call. On the right-hand side, the argument 1.5 is copied into the parameter x. It's used in the calculation and the result gets returned. And that becomes the value of the right-hand side, which is then assigned to y.