Divide a circle into several equal parts and put together an approximate rectangle. The perimeter of the rectangle is 41.4 cm. What is the area of the circle in square centimeters?
把一个圆平均分成若干等份，拼成一个近似的长方形，长方形的周长是41.4厘米，圆的面积是多少平方厘米．
<gadget id="calculator">41.4 / 8.28</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>