Bheja fry question

 Recently I came across this question on Internet.

3     8       10      ???   2    1

6     56      90      20    2      0

This looks quite confusing. 

I don't pressurise myself too much,  since I am not preparing for any competitive exams, 

I let it go. 

I have taken the help of Google  !!!

Let us start solving.... 

Take the numbers given in the first row as 'x'

We can write second row numbers as, 

     y   =    x  ^  2  -   x

According to this, 

Let x be 3

y  =  x ^ 2 - x = 3 ^ 2  - 3  =   9 - 3  =  6

Let x be 8

y  =  x ^2 - x = 8 ^ 2  - 2  =64  - 8 = 56

We can go on Solving for other given numbers. 

Now we know y = 20

We must find out what is x. 

This means,     y  =  x  ^ 2  -   x

==>>      20  =  x  ^  2    -  x

We have only x = 5 which can satisfy the above equation. 

Answer is     5