# Introduction to Functions

In mathematics, the term Function is very famous, if we look in the historical background the term function was first used by very well known Mathematician Leibniz in 1676, who put the meaning of function in term of that dependence of one quantity on another quantity. Function is also known as the input and output machine. Look at some example to clear the concept:

1. Consider the formula for finding the area of circle is $A = \pi {r^2}$, if we look at carefully that the area $A$ of any circle is depend upon the radius $r$ of that circle, we also say that Area $A$ is a function of Radius $r$.
2. A factory worker whose salary may be depending on the number of hours worked. In this example Salary (Amount in Dollar) is function of working hours (Time $t$).
3. The volume of a space occupied by a gas having a constant pressure depends upon the temperature of the gas. In this example Volume ($V$) is a function of Temperature ($T$)

All in above examples, there is a relation between such quantities is often given by means of function.