Observe the graph :

Select the points from the graph and place them in a table.

Table :

Find the difference between the -values and diffrence between -values.

and 

and 

and 

The difference between the –values is , while the difference between the –values is .

Hence the equation is .

Check the solution by substituting -values in the function : 

When ,

When ,

Therefore, the -values are not satisfied the equation.

Let take some other  values to find the equation :

Make a table:

From the table  is always less than .

Therefore, should be subtracted from to get the pattern.

Hence the equation is .

Check the solution by substituting -values in the function : 

When , .

When , .

When , .

When , .

Therefore, the -values are satisfied the equation.

So  the function is .

The funcion is .