This trick must be used for the question where-
1). X should be even number.
2). x should be multiple of two consecutive numbers that is n(n+1)
Where n is first consecutive number and n+1 is second consecutive number and (n+1) will be our answer..

Example-

Q. √56 + √56 + √56 + √56 + .............

first of all calculate the factore of 56 -
7(7+1) = 56
7 + 1 = 8
so 8 will be answer.

Watch Youtube video of Square Root in just 3 second for better understanding.