Jagoan Matematika: Squaring numbers in the 70s

Jagoan Matematika

Gateway For Tour Brain Math

Sunday, May 20, 2007

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:

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

See the pattern?

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

posted by marhadi @ 6:47 AM

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