It may be easier to work backwards, that is, make a chart of integers and their squares. For instance, 1^2 = 1, 2^2 = 4, 3^2 = 9, 4^2 = 16, etc. Then you'll have a list of numbers and their squares that you can reference.
You just need to know the exact trick and formula :D
U can find it fast using differential formula. But normally it will not be accurate. Depends on where ur going to use this calculation. If it is for fast calculation then u can use it.
Ex :
Find the square root of36
36=6 * 6, so X=6
Depends on the worksheet. In general, you should remember that you can factorize the number inside the radical. i.e. sqrt(12)= sqrt(4 x 3)= sqrt(4)*sqrt(3) =2xsqrt(3)