You can also do this by (ab)using the &quot;square of a number close to 50&quot; trick. Take 57^2 for example: this is the square of 50 plus 100 times the difference of the number from 50 plus the square of the difference of the number from 50, which is 2500 + 100x7 + 7^2, or 3249. For 43^2 it would be 2500 + 100x-7 + (-7)^2, which is 2500 - 100x7 + 49, or 1849.<p>With 75, that&#x27;s 2500 + 100x25 + 25^2. Hopefully you&#x27;ve memorized that 25^2 is 625, which makes this an easy 2500 + 2500 + 625, or 5625.