| Sunday, May 20, 2007 |
| Squaring numbers in the 700s |
1. Choose a number in the 700s (practice with smaller numbers, then progress to larger ones).
2. Square the last two digits (keep the carry): _ _ _ _ X X
3. Multiply the last two digits by 14 andadd the carry: _ _ X X _ _
4. The first two digits will be 49 plus the carry: X X _ _ _ _
Example:
1. If the number to be squared is 704:
2. Square the last two digits (keep the carry): 4 × 4 = 16: _ _ _ _ 1 6
3. Multiply the last two digits by 14 andadd the carry: 14 × 4 = 56: _ _ 5 6 _ _
4. The first two digits will be 49 plus the carry: 4 9 _ _ _ _
5. So 704 × 704 = 495,616.
See the pattern?
1. If the number to be squared is 725:
2. Square the last two digits (keep the carry): 25 × 25 = 625: _ _ _ _ 2 5
3. Multiply the last two digits by 14 andadd the carry: 14 × 25 = 10 × 25 + 4 × 25= 250 + 100 = 350. 350 + 6 = 356: 56: _ _ 5 6 _ _
4. The first two digits will be 49 plus the carry: 49 + 3 = 52: 5 2 _ _ _ _
5. So 725 × 725 = 525,625. |
posted by marhadi @ 7:07 AM  |
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