Here is the trick for finding squre of 2 digit number:

* you must remember square from 2 to 9

2 : 4

3 : 9

4 :16

5 : 25

6 : 36

7 : 49

8 : 64

9 : 81

consider we need to find square of AB : 86

here A : 8, B : 6

Step 1:

B²=36 // R1= 6, Carry1= 3

Step 2:

A×B×2 + carry1= 8×6×2 + 3 // R2= 9, carry2= 9

Step 3:

A²+carry2= 73 // R3= 73

Now arrange all Results like R3R2R1= 7396