Huygens' arc length approximation

Christiaan Huygens arc length approximation through the arc height and chord length

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    <title>Huygens' arc length approximation</title>
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    <div class="control">
      <h4><a href="https://en.wikipedia.org/wiki/Christiaan_Huygens" target="_blank">Huygens</a>' arc length approximation</h4>
      <table>
        <tr>
          <td class="name">Angle</td>
          <td id="angle"></td>
        </tr>
        <tr>
          <td class="name">R &times; &theta;</td>
          <td id="classic"></td>
        </tr>
        <tr>
          <td class="name">Huygens</td>
          <td id="huygens"></td>
        <tr>
          <td class="name">Error</td>
          <td id="error"></td>
        </tr>
      </table>
    </div>
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