Principle objective of this lecture is to present on Functions. A function is therefore a many-to-one (or sometimes one-to-one) relation. The set of values at which a function is defined is called its domain, while the set of values that the function can produce is called its range. “f(x) = … ” is the classic way of writing a function. We will see many ways to think about functions, but there are always three main parts: the input, the relationship and the output.