When deriving the formula for the area of a circle, divide the circle into several equal parts and assemble them into an approximate rectangle. Given that the length of the rectangle is 6.28 cm, what is the area of the circle?
在推导圆的面积公式时，将圆等分成若干份，拼成一个近似的长方形．已知长方形的长是6.28厘米，圆的面积是多少．
<gadget id="calculator">6.28 / 3.14</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>