In deriving the area calculation formula, divide the circle into several equal parts and cut them together to form an approximate square. It is known that the perimeter of the rectangle is 20.7 centimeters, and what is the length in centimeters.
在推导面积计算公式，把圆分为若干等份，剪拼成一个近似的产方形，已知长方形的周长是20.7厘米，长是多少厘米．
<gadget id="calculator">20.7 / 8.28</gadget>
<output>2.5</output>

<gadget id="calculator">3.14 * 2.5</gadget>
<output>7.85</output>

<result>7.85</result>