SQUARING A NUMBER ENDING IN 8

Squaring A Number Ending In 8:

   A.  This method  comes from algebra:

(10a – 2)2 = 100(a)(a – 1) + 10(6a) + 4

   B.  Using numbers instead of variables we get the following:

1.  Write down 4.

2.  Add 1 to the ten’s digit and multiply by 6.  Write this number down, carry if necessary.

3.  Multiply the number in the ten’s digit by that number plus 1.  Write this result.

Ex [1]  682 =_________.

a)      Write down 4.

b)      6 x (6 + 1) = 42.  Write 2, carry *4.

c)      6 x (6 + 1) = 42 + *4 = 46.  Write 46.

d)      The answer is 4624.

Ex [2]  1182 =_________.

a)      Write down 4.

b)      6 x (11 + 1) = 72.  Write 2, carry *7.

c)      11 x (11 + 1) = 132 + *7 = 139.  Write 139.   See Multiplying by 11.

d)      The answer is 13924.