4.1 Functions
A function is one of the concepts in math that sounds pretty abstract but is straightforward once you get experience with it. Thought of in terms of numbers, a function takes a value and returns one and only one value. function
For example, for any real number, we can square it. That process is a function from R to R. For any nonnegative real number, if we take the positive square root of it, we get another function. We would not have a function if we were to say we got both the positive and negative square roots.
We use the notation f (x) for a function, meaning we start with some value x, do something to it indicated by the definition of f, and the result is f (x). The f can be any letter or word, but we use f because the word “function” starts with it, and we are not being especially creative. It’s common to see g and h and Greek letters such as γ, but we can use anything that starts with a letter.
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