| Sunday, May 20, 2007 |
| Squaring a 2-digit number ending in 1 |
1. Take a 2-digit number ending in 1.
2. Subtract 1 from the number.
3. Square the difference.
4. Add the difference twice to its square.
5. Add 1.
Example:
1. If the number is 41, subtract 1: 41 - 1 = 40.
2. 40 × 40 = 1600 (square the difference).
3. 1600 + 40 + 40 = 1680 (add the difference twice to its square).
4. 1680 + 1 = 1681 (add 1).
5. So 41 × 41 = 1681.
See the pattern?
1. For 71 × 71, subtract 1: 71 - 1 = 70.
2. 70 × 70 = 4900 (square the difference).
3. 4900 + 70 + 70 = 5040 (add the difference twice to its square).
4. 5040 + 1 = 5041 (add 1).
5. So 71 × 71 = 5041. |
posted by marhadi @ 6:05 AM  |
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