Root 19 x root 19 = 19

Root 19 x root 11 = 1001

Root 11 x root 19 = -1001

Root 11 x root 11 = 11

1001 will cut -1001

It will be left with

19 and -11

Doing the simple arithmetic 

You will have 8

Note 

Root of a number multiplied another root of that same number will give you that number.

The answer= 8