Squaring numbers in the 70s

1. Square the last digit (keep the carry)   _ _ _ X
2. Multiply the last digit by 14, add the carry   _ _ X _
3. The first digits will be 49 plus the carry:   X X _ _

   Example:

     If the number to be squared is 72:

1. Square the last digit:
       2 x 2 = 4     _ _ _ 4
2. Multiply the last digit by 14:
       14 x 2 = 28 (keep the carry)   _ _ 8 _
3. The first digits will be 49 plus the carry:
       49 (+ carry): 49 + 2 = 51  5 1 _ _
4. So 72 x 72 = 5184.

   See the pattern?

     If the number to be squared is 78:

1. Square the last digit (keep the carry):
       8 x 8 = 64 (keep 6)    _ _ _ 4
2. Multiply the last digit by 14, add the carry:
       14 x 8 = 80 + 32 = 112
       112 + 6 = 118 (keep 11)  _ _ 8 _
3. The first digits will be 49 plus the carry (11):
       49 (+ carry): 49 + 11 = 60  6 0 _ _.
4. So 78 x 78 = 6084.