Here are the squares and square roots of all squares up to 31.

1² = 1

2² = 4

3² = 9

4² = 16

5² = 25

6² = 36

7² = 49

8² = 64

9² = 81

10² = 100

11² = 121

12² = 144

13² = 169

14² = 256

15² = 225

16² = 256

17² = 289

18² = 324

19² = 361

20² = 400

21² = 441

22² = 484

23² = 529

24² = 576

25² = 625

26² = 676

27² = 729

28² = 784

29² = 841

30² = 900

31² = 961

Remember,

(1) The last digit of a perfect square is always 0, 1, 5, or 6.

(2) Finding square roots is easier by prime factorisation.

eg. 784 = 2 x 2 x 2 x 7 x 7 x 7

Therefore, the square root of 784 is 2 x 2 x 7, i.e. 28