You&#x27;re saying that<p><pre><code>  x^2 = (50 + (x-50))^2
      = 2500 + 2 * 50 * (x-50) + (x-50)^2
      = 2500 + 100 * (x-50) + (x-50)^2.
</code></pre>
I&#x27;d be a little worried about the number of double-digit squares in this method. I can&#x27;t do them as easily as single-digit squares, which using the multiple of 10 closest to the number ensures.<p>For example, I&#x27;d have to use another trick to calculate<p><pre><code>  13^2 = 100 + 2 * 10 * 3 + 9 = 169
</code></pre>
in the middle of the calculation for<p><pre><code>  63^2 = 2500 + 100*13 + 13^2.
</code></pre>
But<p><pre><code>  63^2 = 3600 + 2 * 60 * 3 + 9 = 3969
</code></pre>
is almost immediate.