Squaring a 2-digit number ending in 6

1. Choose a 2-digit number ending in 6.
2. Square the second digit (keep the carry): the last digit
   of the answer is always 6: _ _ _ 6
3. Multiply the first digit by 2 and add the carry
   (keep the carry): _ _ X _
4. Multiply the first digit by the next consecutive number and
   add the carry: the product is the first two digits:
   XX _ _.

Example:

1. If the number is 46, square the second digit :
   6 × 6 = 36; the last digit of the answer is 6
   (keep carry 3): _ _ _ 6
2. Multiply the first digit (4) by 2 and add the carry
   (keep the carry): 2 × 4 = 8, 8 + 3 = 11; the next digit
   of the answer is 1: _ _ 1 6
3. Multiply the first digit (4) by the next number (5)
   and add the carry: 4 × 5 = 20, 20 + 1 = 21
   (the first two digits): 2 1 _ _
4. So 46 × 46 = 2116.

See the pattern?

1. For 76 × 76, square 6 and keep the carry (3):
   6 × 6 = 36; the last digit of the answer is 6: _ _ _ 6
2. Multiply the first digit (7) by 2 and add the carry:
   2 × 7 = 14, 14 + 3 = 17; the next digit of the answer
   is 7 (keep carry 1): _ _ 7 6
3. Multiply the first digit (7) by the next number (8)
   and add the carry: 7 × 8 = 56, 56 + 1 = 57
   (the first two digits: 5 7 _ _
4. So 76 × 76 = 5776.
   

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