Learn basic math on line

function:A function is a correspondence from a domain set to a range set, where each element of the domain set is related to exactly one element of the range set . 
In other words it can also defined as:
A set is said to be a function if it satisfy the following conditions:

1. Every element of the domain set has image in range set.
2. There is no repetition in the domain  of function.
3. Domain of function must be equal to the domain set.