Let X and Y are two sets. we call a A relation f from X to Y is function if for every x ∈ X there is a unique element y ∈ Y, such that (x, y) ∈ X

We denote it as f: X → Y, which means f is a function from X to Y.

We represent it as-

Example: Let

and

and

Hence it can be represented as-

The expressions of a function we know these days are the standard formulas. for example, if we want tp calculate the area of rectangle, we use Area = length * breadth, here area is the independent variable and l and b are dependent.

when a function contains two or more variables, we call it a multivariable or multivariate function.

## Domain, range and codomain

In a simple language, when all the values go into the function is called domain and the values come out is called range and how many possible values can come out is called the codomain.

**Surjective function (Onto-Mapping)-**

A mapping f: X → Y said to be onto-mapping if the range set

If f: X → Y is onto then each element of B if f-image of at least one element of X. That means.

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